University of Southern California Dissertations and Theses

Binuclear porphyrin and imidazolate bridged complexes as models for cytochrome c oxidase.

(USC Thesis Other)

Binuclear porphyrin and imidazolate bridged complexes as models for cytochrome c oxidase.

PDF

Download a page range

Download transcript

Copy asset link

Request this asset

Transcript (if available)

Content BINUCLEAR PORPHYRIN AND
IMIDAZOLATE BRIDGED COMPLEXES AS
M ODELS FOR CYTO CHRO M E C OXIDASE
by
Carol Ann Koch 1
A Dissertation Presented to the
FACULTY O F THE GRADUATE SCHO O L
UNIVERSITY O F SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTO R O F PHILOSOPHY
(Chemistry)
December 1988
Copyright 1988 Carol Ann Koch
UMI Number: DP21972
All rights reserved
INFORMATION TO ALL USERS
The quality of this reproduction is dependent upon the quality of the copy submitted.
In the unlikely event that the author did not send a complete manuscript
and there are missing pages, these will be noted. Also, if material had to be removed,
a note will indicate the deletion.
Dissertation Publishing
UMI DP21972
Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author.
Microform Edition © ProQuest LLC.
All rights reserved. This work is protected against
unauthorized copying under Title 17, United States Code
ProQuest LLC.
789 East Eisenhower Parkway
P.O. Box 1346
Ann Arbor, Ml 48106-1346
UNIVERSITY OF SOUTHERN CALIFORNIA
THE GRADUATE SCHOOL
UNIVERSITY PARK
LOS ANGELES, CALIFORNIA 90089
under the direction of h.^S...... Dissertation
Committee, and approved by all its members,
has been presented to and accepted by The
Graduate School, in partial fulfillment of re
quirements for the degree of
This dissertation, written by
Garol Ann Koch
DO CTO R OF PHILO SO PHY
Dean of Graduate Studies
Date December 7, 1988
DISSERTATION COMMITTEE
Chairperson
This work is dedicated
to m y husband Mike
who was behind m e
all the way.
Acknowledgments
There so many people who have helped m e through this work and
even though I can not mention them a ll, I w ill not forget them.
Special thanks to . . .
...my research advisor, Chris Reed, for the ideas and the means to
execute them and for helping m e grow.
...John Tate for getting m e started.
...Gerry Wuenschell for answering a ll m y questions.
...Bob Scheidt for the crystal structures solved and the countless
others.
...Robert Orosz and Darren Baldwin for th e ir computer expertise.
...David Liston for KBr pellets and helium cylinders.
...T erry W en for listening.
...Dave Chapman for laughs.
...Ray Stevens for never giving up on m y crystals and for keeping m e on
m y toes.
...R odj, the one who helped m e and hurt m e the most.
...M .A. Patch for the lab space and C O I borrowed, and for getting m y
p rio ritie s straight.
...Malcolm McLean for keeping m e sane and smiling.
Table of Contents
Dedication
Acknowledgments
List of Figures
List of Tables
Abstract
Chapter 1. Introduction
The Protein Structure
Metal Centers
Properties of Cytochrome a and Cu/\
Properties of Cytochrome 33 and Cur
Imidazolate Bridge
Oxygen Bridge
Sulfur Bridge
Carboxyl ate Bridge
Other Models
Alternative Theories
Our Approach
References
Chapter 2. Pincer Porphyrin
Ligand Design Strategy
Synthesis of Pincer Porphyrin
Characterization
Experimental
Summary
References
Chapter 3. Copper Complexes of Pincer Porphyrin
Metalation of the Porphyrin
Coordination of Upstairs Copper
Experimental
Summary
References
Chapter 4. Iron Complexes of Pincer Porphyrin
Synthesis and Characterization of Fe(PincerP)(THF)2
Carbon Monoxide A ffin ity
V
Ir o n (III) Complexes 89
Reactions with Copper(I) Hexafluorophosphate 93
Reactions with Copper(I) T rifla te 95
Reactions with Copper(I) Chloride 99
Reactions with Copper(I) Cyanide 100
Experimental 105
Summary 114
References 115
Chapter 5. Imidazolate Bridged Complexes 117
Experimental 121
Metal Imidazolate Complexes 127
Iro n (II) Bis-Metal Imidazolate Complexes 132
Ir o n (III) Bis-Metal Imidazolate Complexes 133
Manganese(II) Metal Imidazolate Complexes 146
Capped Porphyrin Metal Imidazolate Complexes 147
Summary 156
References 165
Selected Bibliography 168
List of Figures page
Figure 1-1. Schematic representation of y-shaped cytochrome
c oxidase........................................................................................................................... 4
Figure 1-2. The chemical structure of heme a, the iron porphyrin
found in cytochrome c oxidase................................................................................. 5
Figure 1-3. Proposed structure of the active site of cytochrome c
oxidase incorporating an imidazolate bridge.................................................10
Figure 1-4. Examples of homobinuclear imidazolate bridged compounds figure 1-4. txampies of homoDinuciear imidazolate bridged compoun<
which exhibit a) moderate anti ferromagnetic coupling (-J=81.3cm"l)
(from reference 31) and b) weak anti ferromagnetic coupling
(-J=8+2cnT*) (from reference 3 5 ).........................................................................12
Figure 1-5. Fe(UroTPP)Cu(acac)2, an example of a heterobinuclear
imidazolate bridged complex which shows no coupling of the metals
(from reference 3 8 )..................................................................... ..............................13
Figure 1-6. Proposed structure of Wilson's manganese/copper
imidazolate bridged complex, [Mn(TPP)Cu(imid)] BF4 , (from
reference 41 )............................................................................ . ..................................13
Figure 1-7. Proposed structure of the active site of cytochrome c
oxidase incorporating a fi-oxo bridge.................................................................15
Figure 1-8. Schematic drawing of the thiazole strapped porphyrin
synthesized by Chang and co-workers...................................................................17
Figure 1-9. A view of E llio tt's [Fe(TPP)(THF)] [Cu(MNT)2] " anion,
where M NT = c/s-l,2-dicyanoethylene-l,2-dithialato, TPP = te tra -
phenyl porphyrin, and THF = tetrahydrofuran..................................................18
Figure 1-10. Possible structure of carboxyl ate bridged
Fe(TPP)Cu(aibi), where aib3 is the tripeptide of a-aminoiso-
butyric acid (from reference 61) .........................................................................19
Figure 1-11. A view of the [Fe(P)-Cl-Cu(N4 )]^+ cation from
Gunter's meso-a,or,a,o;-tetra(o-nicotinamidophenyl) porphyrin.................. 20
Figure 2-1. Schematic drawing of pincer porphyrin, a binucleating
ligand capable of holding two metals in close proximity........................ 31
Figure 2-2. S tatistical mixture of the four atropisomers of
tetra(o-ami nophenyl) porphyri n............................................................................... 35
Figure 2-3. Reaction of four up amino with t r it y l bromide to
form the mono-, c /s -d i-, trans-di-, and t r i - t r i t y l products................37
V I 1
Figure 2-4. Reaction of four up amino with 4 , 4 ' , 4 " -tris(ben-
zoyloxy)tritylbromide results in minor fractions of the mono- and
t r i - t r i t y l products, as well as the cis- and trans-d i t r i t y l ................39
Figure 2-5. Acetic acid and 4,5-o-phenylenediamine are condensed
to form 2,5,6-trimethylbenzimidazole.................................................................40
Figure 2-6. 90MHz N M R of pincer porphyrin in CDCI3 .......................... 42
Figure 2-7. Tautomerism of the central porphyrin protons...................43
Figure 3-1. The Cu(PincerP) molecule viewed from above the
porphyrin plane.............................................................................................................56
Figure 3-2. The Cu(PincerP') molecule viewed from above the
porphyrin plane.............................................................................................................57
Figure 3-3. Portion of Cu(PincerP') molecule shown to illu s tra te
the hydrogen bonding between the picket amide and the benzimidazole
nitrogen lone p a ir...................................................................................................... 58
Figure 3-4. Vibrational spectrum (KBr p ellet) of
Cu(PincerP) ‘3CHC1 3 ...................................................................................................... 61
Figure 3-5. Vibrational spectrum (KBr p ellet) of
[Cu(PincerP)Cu]PFg...................................................................................................... 62
Figure 3-6. Vibrational spectrum (KBr pellet of
[Cu(PincerP)Cu]C1 0 4 ................ 63
Figure 3-7. Vibrational spectrum (KBr pellet of
[Cu(PincerP)Cu]BF4 ...................................................................................................... 64
Figure 3-8. Vibrational spectrum (KBr pellet of
deuterated Cu(PincerP).3CDCI3 ...............................................................................66
Figure 3-9. Side view of the [(DMF)Zn(PincerP')Cu]PFg molecule 68
Figure 4-1. A view of the Fe(PincerP') (l-t-Bulm) molecule where
l-t-Bulm = 1-t-butyl imidazole............................................................................... 76
Figure 4-2. Visible spectrum of Fe(PincerP) in THF (top) and
benzene (bottom)...........................................................................................................77
Figure 4-3. Vibrational spectrum (KBr p e llet) of
Fe(PincerP)(THF) 2 ........................................................................................................ 79
Figure 4-4. Truth diagram for Mossbauer parameters of iron
porphyrins.......................................................................................................................81
viii
Figure 4-5. Series of visible spectra of Fe(PincerP) in a
toluene solution of 1,2-dimethyl imidazole......................................................85
Figure 4-6. Data and graph used for the determination of
P l/2C O for Fe(PincerP)..............................................................................................86
Figure 4-7. Vibrational spectrum (Nujol mull under CO) of
Fe(PincerP) ( 1 , 2 -Me2 lm) (CO)......................................................................................88
Figure 4-8. Visible spectrum in THF of Fe(PincerP)Cl (top),
Fe(PincerP)OH (center), and [Fe(PincerP) ] 2 0 (bottom)...............................90
Figure 4-9. Vibrational spectrum (KBr p e lle t) of [Fe(PincerP) ] 2 0
(top), Fe-O-Fe stretch at 865cm"1, and Fe(PincerP)OH (bottom),
O H bend at 1400cm'1....................................................................................................92
Figure 4-10. Visible spectrum in THF of reaction of
Fe(PincerP)(THF)? and Cu(MeCN)dPF5 before (top) and after
(bottom) crystallizatio n from THF and methanol........................................... 94
Figure 4-11. Vibrational spectrum (KBr p e llet) of product from
reaction of Fe(PincerP)CO and copper(I) t r if la t e afte r being
put under vacuum to remove CO............................................................................... 97
Figure 4-12. Vibrational spectrum (KBr p e llet) of product from
reaction of Fe(PincerP)(THF)? and CuCN in THF............................................101
Figure 4-13. Vibrational spectrum (KBr p e llet) of
[Fe(PincerP)(CN)]Et4N.............................................................................................. 103
Figure 5-1. Schematic drawing of metal imidazolate complexes
where M = Cu, N i.........................................................................................................120
Figure 5-2. Plot of effective magnetic moment vs. temperature
for Nilm..........................................................................................................................128
Figure 5-3. Plots of reciprocal molar susceptibility and
effective magnetic moment vs. temperature for (Culm)?............................. 130
Figure 5-4. Plot of effective magnetic moment vs. temperature
for Fe(TPP)(NiIm)2 ‘ 2toluene..................................................................................134
Figure 5-5. Plots of reciprocal molar susceptibility and
effective magnetic moment vs. temperature for
Fe(TPP)(CuIm)2 *2toluene..........................................................................................136
Figure 5-6. Plots of reciprocal molar susceptibility (triangles)
and effective magnetic moment (circles) vs. temperature for
[Fe(TPP)(NiIm)2 3 (B11CH12) - 5THF........................................................................... 140
ix
Figure 5-7. Plots of reciprocal molar susceptibility and
effective magnetic moment vs. temperature for
[Fe(TPP)(CuIm)2 ](B11CH12)*5THF........................................................................... 142
Figure 5-8. A view of the [Fe(TPP)(Culm)2 ](BuCHi2 )-4DMF
molecule..........................................................................................................................144
Figure 5-9. Alternate view of two [Fe(TPP)(CuIm)](BuCHi2 )*4DMF
molecules showing the interaction between adjacent copper centers.145
Figure 5-10. Plots of reciprocal molar susceptibility (triangles)
and effective magnetic moment (circles) vs. temperature for
M n (TPP) (Ni Im) • 3tol uene............................................................................................148
Figure 5-11. Plots of reciprocal molar susceptibility and
effective magnetic moment vs. temperature for
Mn(TPP) (Culm)-tol uene.............................................................................................. 150
Figure 5-12. Plots of reciprocal molar susceptibility
(triangles) and effective magnetic moment (circles) vs.
temperature for Mn(TPP) (l-Melm) .............................................................152
Figure 5-13. Schematic drawing of Baldwin's capped porphyrin
(from reference 26 ).................................................................................................. 155
Figure 5-14. Plot of magnetic moment vs.
temperature for [Fe(C2Cap) (Ni Im)] ( BjjCHi2) *4THF....................................... 157
Figure 5-15. Plot of reciprocal molar susceptibility vs. temp
erature for [Fe(C2Cap)(NiIm)](Bn CH12)*THF..................................................158
Figure 5-16. Plot of effective magnetic moment vs. temperature
for [Fe(C2Cap) (Culm)] (Bn CH12) -THF...................................................................160
Figure 5-17. Plot of reciprocal molar susceptibility vs. temp
erature for [Fe(C2Cap)(Culm)](BuCHi2)-THF..................................................161
X
List of Tables
Table 4-1. Mossbauer parameters for iron porphyrins.............................82
Table 5-1. Variable temperature magnetic susceptibility data
for Nilm in 10KG magnetic f ie ld ......................................................................... 129
Table 5-2. Variable temperature magnetic susceptibility data
for (Culm)2 in 10KG magnetic f ie ld ...................................................................131
Table 5-3. Variable temperature magnetic susceptibility data
for Fe(TPP) (Ni Im)2 *2toluene in 10KG magnetic f ie ld ................................. 135
Table 5-4. Variable temperature magnetic susceptibility data
for Fe(TPP) (CuIm)2 ’ 2toluene in 10KG magnetic f ie ld ................................. 137
Table 5-5. Variable temperature magnetic susceptibility data
for [Fe(TPP)(NiIm)2 3 (B11CH12 ) * 5THF in 10KG magnetic f ie ld .................141
Table 5-6. Variable temperature magnetic susceptibility data
for [Fe(TPP)(Culm)2 ](B11CH12) *5THF in 10K G magnetic f ie ld .................143
Table 5-7. Variable temperature magnetic susceptibility data
for Mn(TPP)(NiIm)-3toluene in 10KG magnetic f ie ld ................................... 149
Table 5-8. Variable temperature magnetic susceptibility data
for Mn(TPP) (Culm)-toluene in 10KG magnetic f ie ld ......................................151
Table 5-9. Variable temperature magnetic susceptibility data
for Mn(TPP)(l-Melm) in 10KG magnetic f ie ld ..................................................153
Table 5-10. Variable temperature magnetic susceptibility data
for [Fe(C2Cap)(NiIm)](B11CH12 ) * 4THF in 10KG magnetic f ie ld ................ 159
Table 5-11. Variable temperature magnetic susceptibility data
for [Fe(C2Cap)(CuIm)](B11CH12)-THF in 10KG magnetic f ie ld .................162
xi
Abstract
The aim of this work was to produce model compounds designed to
mimic the active site of cytochrome c oxidase, the terminal enzyme of
the electron transport system responsible for the reduction of oxygen
to water. The active site of the resting form of the enzyme is known
to contain F e (III) and C u(II) metal sites whose ESR silence may be due
to strong anti ferromagnetic coupling with -J>200cm- ^.
The f ir s t strategy towards producing model compounds was the
synthesis of a binucleating porphyrin ligand, pincer porphyrin,
a ,a ,5 ,1 5 -b is [ N - (2 ,5 ,6 -t r im e t h y lb e n z im id a z o ly l) acetamidophenyl] -
a,a,10,20-bis-(pivalamidophenyl)porphine. This synthesis represents
the f ir s t trans-difunctionalized tetraaryl porphyrin and was achieved
with the use of the bulky protecting groups triphenylmethyl and
4 , 4 ' , 4 " -tris(benzoyloxy)triphenylmethyl. The mononuclear copper
complex, Cu(PincerP)'3CHCI3 , was synthesized and its x-ray crystal
structure presented. Also prepared was a series of binuclear copper
complexes, [Cu(PincerP)Cu]X, where X = PFg, BF4 , CIO4 , and O 3 SCF3 .
Metalation of pincer porphyrin with iron resulted in the bis-THF
complex Fe(PincerP)(THF) 2 which, along with its oxidation products
[Fe(PincerP) ] 2 0 and Fe(PincerP)OH, was characterized. Reactions of the
ferrous and fe rric porphyrins with various Cu(I) salts resulted in 1:1
Fe/Cu complexes, however, these failed to yield x-ray quality crystals.
Secondly a series of binuclear and trinuclear imidazolate bridged
compounds w ere s y n th e s iz e d in c lu d in g F e ( T P P )(M Im )2 »
[Fe(TPP)(MIm)2 ](Bn CH12), Mn(TPP)(MIm), and [Fe(C2Cap)(MIm)](Bn CH12)
xi i
where M = Cu or Ni, TPP = tetraphenylporphyrin, and C2Cap = Baldwin's
capped porphyrin. The magnetic properties of each compound were
studied. The ir o n ( III) bis-imidazolate complex is the f ir s t example of
a ferromagnetically coupled (J=10cm“l) imidazolate bridged complex.
Its x-ray crystal structure has also been determined. The M n(II) and
F e (III) mono-imidazolate complexes both show weak anti ferromagnetic
coupling with J=-6 and -20cm- ^, respectively. This work supports the
proposal that imidazolate is not capable of mediating strong
anti ferromagnetic coupling such as the -J>200cm~^ coupling presumed
for the active site of cytochrome c oxidase.
1
Chapter 1
Introduction
The reduction of oxygen to water is an apparently straightforward
chemical reaction (O2 + 4H+ + 4e' — > 2H2O), yet when placed in the
context of biological systems i t becomes a complex process. The
catalyst which drives this reaction, cytochrome c oxidase, is a well
studied yet incompletely understood enzyme. I t has intrigued
researchers for over a century provoking investigations from many
d ifferen t viewpoints, but its structure and the mechanism by which i t
catalyzes this reaction remain unsolved.
The importance of cytochrome c oxidase stems not only from the
fact that i t is the enzyme of oxygen reduction in a ll animals, in
plants, yeasts and some bacteria, 1 and that 90% of a ll oxygen consumed2
by aerobic l i f e is eventually reduced by cytochrome c oxidase, but also
from the fact that this reaction is in trin s ic a lly linked to the
formation of ATP (adenosine triphosphate) which is the source of energy
for biochemical reactions. 3 It is this coupling of two major
I processes, oxidation and phosphorylation, which makes the elucidation!
I 1
'o f this enzyme's structure and mechanism so complex and v ita l to our
i understanding of biological systems.
; The oxidation of foodstuffs produces electrons which are
! transferred through a number of enzymes known as the electron transport:
; system or respiratory chain. 4 This chain consists of three main enzyme;
complexes, NADH-ubiquinone reductase, ubiquinol cytochrome c reductase,
J
and cytochrome c oxidase. These in turn are made up of smaller
electron carriers such as iron-sulfur complexes, quinones, and
■cytochromes or heme containing proteins, whose reduction potentials
! increase sequentially. Being the terminal enzyme complex of the
jrespiratory chain, cytochrome c oxidase is responsible for transferring
; electrons to molecular oxygen, which has been absorbed, or in mammalian
1 systems, transported via hemoglobin. Due to the exothermicity o f
; oxygen reduction, cytochrome c oxidase is capable of displacing protons
from the matrix side of the mitochondrial membrane to the cytoplasmic
side (Figure 1-1). At the same time protons on the matrix side are
being consumed by the formation of water. This proton pump5 generates
an electrochemical gradient which produces the required energy to drive
the phosphorylation of ADP forming ATP. Oxidative phosphorylation is
responsible for close to 90% of the total ATP produced. 4
The Protein Structure
Cytochrome c oxidase is d iffic u lt to study because of its large
size and the fact that i t is membrane bound. In mammalian cells the
I
I
enzyme is bound to the inner membrane of the mitochondria, while in
bacteria i t is part of the plasma membrane. In both cases isolation;
and purification are complicated since i t can only be separated from
the membrane by treatment with detergents. This process leads to
varying degrees of purity so that determination of molecular weight and
I
subunit composition are d iffic u lt and results have varied depending on
the experimental methods used. Bacterial cytochrome c oxidases are
re la tiv e ly small consisting of two or three subunits, 6 while yeast
enzymes contain seven or eight. Molecular weights of over 200kDa are
found in beef heart cytochrome c oxidase which is made up of thirteen
polypeptide chains. 7
Electron microscopy of bovine cytochrome c oxidase crystals8 * 9
shows the 13 subunits arranged in an unsymmetrical Y-shaped group
traversing the lip id bilayer of the mitochondrial membrane (Figure 1-
1). The two tips extend inside the membrane into the matrix and
protrude approximately 20A. The major portion of the protein is
contained in the stem which crosses the membrane and extends
approximately 50A into the cytoplasmic side of the mitochondrion. This
large section of the enzyme allows room for binding of the electron
donor, cytochrome c, and possibly oxygen. The primary structure of the
subunits from several sources has been determined, and the sequence of
amino acids is highly conserved. 10 Most subunits consist of
alternating hydrophobic and hydrophilic segments which indicates that
the protein bends back and forth across the membrane several times,
with the hydrophilic segments remaining on the surface of the membrane.
Q
outer membrane
cytoplasm
Cytc
ox
Cyt c
red
» inner » /
membrane
Cu
- 6-
matrix
ADR + Pj —> ATP
Figure 1-1. Schematic representation of y-shaped cytochrome c oxidase.
The combination of protons being pumped to the cytoplasmic side and
protons being consumed 1n the formation of water leads to an
electrochemical gradient across the membrane.
Metal Centers
j
! The most intriguing aspect of the enzyme from a bioinorganic
)
i
<
Viewpoint is the fact that i t contains four redox-active metal centers:
|two iron atoms in the form of heme a (Figure 1-2) and two copper
i
atoms.
H O -CH CH
C H
C H
CH CH
c h 2 c h 2
COOH COOH
[Figure 1-2. The chemical structure of heme a, the iron porphyrin found*
|in cytochrome c oxidase. |
i I
j All four metal sites are confined to subunits I and I I of the!
| j
protein and are involved in the fin al steps of electron transfer. In
order to understand the mechanism by which four electrons are
transferred to molecular oxygen, the structural and electronic
environments of the four metal centers must be investigated. There is
jgeneral agreement that each metal site is capable of accepting a single
electron so that the oxidation states of interest are F e (II) and
Fe( I I I ) , and Cu(I) and C u (II). The resting state of the enzyme is the
fu lly oxidized or Fe( I I I) /C u ( II ) state. The properties of the
differen t states of the enzyme (fu lly oxidized, p a rtia lly reduced, and
fu lly reduced) have been investigated as have those formed by the
introduction of small ligands (CO, CN, and NO) whose presence
influences the spectroscopic properties of the metal sites.
Even though the porphyrin ligand of both iron atoms is the same,
these metals display distinct properties. They are referred to as
cytochromes a and 8 3 . Sim ilarly, the two copper atoms are in unique
environments and are labeled C u/^ and Cug. The function of each metal
allows them to be divided into pairs. Cytochrome a and Cu^ are
responsible for electron transport from cytochrome c, the preceding
electron carrier in the respiratory chain, to the cytochrome 3 3 , Cug
pair. This is the binding site of oxygen and is therefore referred to
as the active site of the enzyme.
Recent investigations have also shown the presence of zinc, and
magnesium, 11 both in ratios of 1:2, M:Fe. While the functions of the
two metals is unknown, i t is believed to be structural rather than
cataly tic . This is supported by the fact that removal of zinc does not
affect the catalytic a c tiv ity of the enzyme. 12
Properties of Cytochrome a and Cu/\
Cytochrome a is the simplest metal center in the enzyme. I t is a
six-coordinate, low spin heme in both the reduced and oxidized forms. 13
Its M C D and EPR spectra14’ 15 clearly indicate a low spin state, and the
fact that i t does not bind carbon monoxide, cyanide or azide suggests
that i t already contains ligands in the f if t h and sixth positions.
The presence of two axial imidazole ligands is shown by comparison of
the resonance Raman spectra16 and the EPR g-values (3.0, 2.2, and 1.5)
with low spin fe rric heme a compounds of known axial lig a tio n . 17
The remaining EPR signals of the resting state enzyme13 (g=2.18,
2.03, and 1.99) have been assigned to Cu/^. The unusually low g values
(one is even less that the free electron g value) are unique to this
copper and are thought to be due to an unusual geometry and
coordination about Cu/\. The lack of hyperfine structure in these
signals is also atypical of copper and indicates delocalization of the
unpaired electron onto the surrounding ligands. This suggests at least
one and possibly two cysteine sulfur ligands18 which is supported by
EXAFS measurements19* 20 showing 2-3(S) ligands and 1-2(N,0) ligands in
the f ir s t shell of copper. A puzzling aspect of the EPR signals is
that th e ir combined intensity consistently accounts for less than 40%
of the copper present in the enzyme. There have been several
explanations of this apparent anomaly: (1) The method of purification
could cause adventitious copper to be present in the enzyme. (2) A
third copper atom has been found in bacterial and bovine cytochrome c
oxidase using inductively coupled plasma atomic emission spectroscopy21
and i f present in its cuprous oxidation state, i t would be EPR s ile n t.
(3) The decreased intensity of the EPR signal could be caused by
coupling of Cu/\ with another paramagnetic center, possible heme a. 18
ENDO R studies13* 18 on isotopically labelled derivatives of the
enzyme show coupling between Cu^ and both deuterated cysteine and
substituted histidine, and therefore indicate at least one histidine
and one cysteine ligand. The primary structure10 of subunit I I
contains two invariant cysteines (Cys225 and Cys229) and one histidine
(His233) in a short segment corroborating the EPR and ENDO R evidence.
The fourth ligand to Cu^ has been suggested to be a second h istid ine22
(there are two more invariant histidines in subunit I I ) however there
is no strong evidence for this and water (or hydroxyl ion) has been
imp!icated. 18
As mentioned previously the function of both cytochrome a and Cu/\
is electron storage and transport. Cytochrome a is the primary
electron acceptor of the enzyme, receiving electrons via cytochrome c
which binds on the cytoplasmic side. The electrons are then either
transferred to Cu^ or in conjunction with Cu^ are passed on to the
active s it e . 23 The distance between these metal centers13 is
approximately 10A and both are at least that fa r from the cytochrome
a3/CuB pair.
Properties of Cytochrome 33 and Cug
As the active site of the enzyme, the cytochrome a3/CuB complex is
the key to understanding the four electron reduction of oxygen to
water. In trin sic to resolving the mechanism of cytochrome c oxidase is
a detailed knowledge of the structure of its active s ite. Therefore
elucidation of the geometry and ligand environments of both these metal
centers is of utmost importance as is th e ir relationship to one
another.
The most remarkable aspect of this metal pair is that like
cytochrome a and Cu/\ they are present in fe rric and cupric oxidation
states in the resting enzyme, and yet both are EPR s ile n t. Heme a$ is
a high spin Fe( I I I ) (S=5/2) while Cug is present as Cu( I I ) (S =l/2).
j Both should show distinctive EPR signals however only heme a and Cu/\
\
\ signals are accounted for in the EPR spectrum. The original
Explanation for this unusual observation was that heme 33 and Cug are
antiferromagnetically coupled2 4 ’ 15 producing an S=2 ground state which
is EPR s ilen t. Subsequent studies on the magnetic susceptibility25 of
cytochrome c oxidase agreed with an S=2 ground state and suggested that
since this state persisted even at room temperature, the coupling was
presumed to be very strong with -J>200cm"E
Manipulations on the enzyme can lead to EPR signals. For example,
the p a rtia lly reduced form shows a high spin heme EPR signal at g=6 .
Also, addition of n itric oxide to the fu lly reduced enzyme gives EPR
signals13 typical for nitrosylferrohemes. The hyperfine sp littings of
this spectrum indicate that the f if t h axial ligand of heme 33 is
imidazole from histidine. This fact was proven by EPR studies on the
N O adduct of the yeast enzyme containing labelled h is tid in e. 26
Addition of N O to oxidized cytochrome c oxidase gives signals
characteristic of high spin heme indicating that exogenous ligands can
bind to Cug as we^ as heme a3 * The nature of the ligands coordinating
CU3 is uncertain. ENDO R measurements27 revealed the presence of three
nitrogen ligands which is consistent with one interpretation of EXAFS
data19 showing 4(N,0). However, another EXAFS group20 concluded that
the f ir s t shell of Cub contained 2 (N,0 ) and 1 (S, Cl) and the most recent
data28 on Cu/\ depleted enzyme indicates 3(N,0) and 1 (S, C l). I t is not
10
possible to distinguish between N and 0 or between S and Cl 1n EXAFS
experiments. The nitrogenous ligands are generally believed to be
imidazoles from histidines while the sulfur ligands could be cysteine
or methionine.
In order to ju s tify the strong coupling between cytochrome a$ and
Cu{j, the presence of a bridging ligand has been invoiced. There is no
direct evidence of the existence or the nature of this bridging ligand
and several theories have been proposed.
Imidazolate Bridge
j
The f ir s t suggestion for a bridging ligand between cytochrome a$
and Cub was imidazolate, 24 as shown in Figure 1-3. The presence ofj
imidazole as an axial ligand to cytochrome a$ has been proven by E P R I
!
studies previously discussed, however whether this ligand is proximal!
(between iron and copper) or distal (on the side of the heme opposite!
j
to copper) has not been determined. j
I I
I I
\
Figure 1-3. Proposed structure of the active site of cytochrome c
oxidase incorporating an imidazolate bridge.
The existence of an imidazolate bridge between metals in!
j
jbiological systems is not without precedent. I t is known that Znl
I
superoxide dismutase29 contains an imidazolate bridge between Z n (II)
11
and Cu( I I ) , and the cobalt substituted enzyme30 exhibits moderate
anti ferromagnetic coupling (-J=66 cm“l) between C o(II) and C u (II).
There have been numerous attempts to mimic biological systems
containing an im idazolate bridge. Both homobinuclear and
heterobinuclear model compounds have been synthesized and th eir
spectral and magnetic properties studied in order to determine the
a b ility of imidazolate to mediate anti ferromagnetic coupling between
two metals.
Homobinuclear models31" 34 of the type Cu( I I ) - Im -Cu(II) have shown
significant anti ferromagnetic coupling with -J=0.5-90 cm'*, while face-
to-face porphyrins3 5 * 36 of F e (II) and M n(II) show coupling much lower,
-J^2cm'l (Figure 1-4).
Heterobinuclear model compounds containing two d ifferen t metal
centers exhibit varying magnetic properties. Weak coupling exists in
the face-to-face porphyrin36 containing M n(II) and C o(II) (-J=5cm“l) as
in its homonuclear analogues. M n (II), being isoelectronic with high
spin Fe( I I I ) , is often used as a spin model for cytochrome c oxidase.
Likewise, C o(II) mimics the Cu{ I I ) s ite .
Cutler et a l37 followed the reaction of a water soluble iron
porphyrin, sodium tetra-p-sulfophenylporphine i r o n ( III) with a
trip e p tid e copper complex, copper(II)glycylglycyl-L-histidine-N -
methylamide. Upon analysis of the solution EPR spectrum they concluded
the iron was present in its intermediate spin state, (S=3/2). They
were unable to isolate the product in order to obtain magnetic
susceptibilities or structural data. Models containing Fe( III) - Im -
Cu ( I I ) centers have been synthesized which show no coupling what
12
soever. Prosperi and Tomlinson38 reacted Fe(TTP)(2 -MeIm)2Cl with
Cu(acac)2 » while Saxton and Wilson39 used Fe(UroTPP)Cl (Figure 1-5)
with the same Cu complex and in both cases no interaction between the
metal centers occured.
Wilson et a l4 0 »41 have described the reactions of M n(II) and
F e (III) tetraphenylporphyrins with C u(II) imidazolate complexes. (See
Figure 1-6.) The lowered magnetic moments and EPR silence of the
Figure 1-4. Examples of homobinuclear imidazolate bridged compounds
which exhibit a) moderate anti ferromagnetic coupling (-J=81.3cm'4)
(from reference 31) and b) weak antiferromagnetic coupling (-J=8+2cm'1)
(from reference 35). Oval represents the porphyrin macrocycle.
_ _ 13
products have been rationalized by strong anti ferromagnetic coupling.
i
jHowever, the conclusions are not d e fin itiv e as there are alternative
i
[explanations for the magnetic and spectral data. For example, the
'CO
NH
Fe
| Figure 1-5. Fe(UroTPP)Cu(acac)2 , an example of a heterobinuclear
» imidazolate bridged complex which shows no coupling of the metals (from
j reference 38).
1 +
Cu
Mn
I Figure 1-6. Proposed structure of Wilson's manganese/copper
imidazolate bridged complex, [Mn(TPP)Cu(imid)]BF4 , (from reference 41).
magnetic moment (/*eff= 5 .11/ig) of the Mn/Cu complex could equally be
explained by ferromagnetic coupling between H n (II) (S=3/2) and Cu( I I )
(S=l/2) or by no coupling between the same centers.
The a b ility of the imidazolate anion to bridge two metal centers
and provide a pathway for anti ferromagnetic coupling has been proven by
a variety of model compounds, but whether this bridge is capable of
producing the strong coupling on the order of -J>200cm'l which may be
present in cytochrome c oxidase has not been unambiguously determined.
The Fe-Cu distance of the active site in cytochrome c oxidase is
uncertain, but i t has been estimated using various techniques.
Analysis of EPR data on the N O adduct26 puts the cytochrome a3/Cug
distance at approximately 5A, while interpretation of various EXAFS
results d iffe rs greatly. One group20 estimates the distance at
3.75+0.05A, while another group19 concludes that Fe and Cu are
3.02+0.02A apart. I t should be noted that an imidazolate bridge
between cytochrome a3 and Cug would necessitate an Fe-Cu separation of
about 6A and a distance this large would be undetectable by EXAFS.
. Oxygen Bridge
An alternative hypothesis for the active site of cytochrome c
oxidase consists of a n~oxo bridge17’ 42’ 43 between cytochrome 33 and
Cug. Support for this theory is based on several precedents. Other
bim etallic enzymes are believed to contain jjl- oxo bridges at th e ir
active sites. Hemerythrin consists of a high spin F e (III) dimer
bridged by a single oxygen atom and two carboxylate groups, while
hemocyanin contains a C u(II) dimer bridged by dioxygen and a second
single atom bridge which is presumably /i-oxo. In both cases the metals
are strongly antiferromagnetically coupled. 44
Model compounds of homonuclear M-O-M centers are known to exhibit
strong coupling. For example porphyrin fi-oxo dimers such as
[ Fe(TPP)]2O and [Fe(protoporphyrin IX )] gO contain iron centers which
are antiferromagnetically coupled with -J values of 100 and 131cm"^
respectively. 45
Figure 1-7 shows the proposed active site of cytochrome c oxidase
with a (i-oxo bridge. The imidazole as sixth ligand to cytochrome 33)
may not be bound in the resting state of the enzyme. The presence ofj
i
the axial imidazole was proven in the reduced form and assumed present!
!
in the oxidized form, but since /i-oxo F e ( III) porphyrins are typicallyj
I
5-coordinate the po ssibility exists that the distal histidine is not
ligated in the resting form of the enzyme.
- • f 1 ,h Cu1 1
O '
H
Figure 1-7. Proposed structure of the active site of cytochrome c
oxidase incorporating a /i-oxo bridge. The distal imidazole from
histidine may or may not be coordinated to iron.
I f the Fe-Cu distance derived from EXAFS data is correct j
I
(3.0-3.8A) the single atom oxygen bridge is a more lik e ly candidate:
I
for the active site of cytochrome c oxidase since, as mentioned !
16;
previously, a /*-imidazolato ligand would require a greater separation
between the two metals.
Isotopic exchange experiments have been conducted on cytochrome c
oxidase in order to probe the existence of a fi-oxo bridge. Resonance
Raman spectroscopy46 was used to study *80 substituted enzyme in the
hope that a change in the spectrum would id entify vibrations of
cytochrome 3 3 . The fact that no change was observed indicates, but
does not prove, that a fi-oxo bridge is not present. S im ilarly, enzyme
allowed to reduce * 802 failed to retain any of the isotopically
labelled oxygen after a single turnover, 47 suggesting that an oxygen
bridge is not formed during the catalytic cycle. However, the
possibility exists that the fi-oxo bridge exchanges rapidly with bulk
solvent water which would explain the lack of * 80 retention by the
enzyme. Reoxidation of the reduced enzyme in the presence of H2 ^ 0
also showed no effect on the EPR spectrum48 suggesting that a la b ile
oxygen ligand does not exist in the active site .
There have been two attempts to mimic the F e (III)-0 -C u (II) active
site of cytochrome c oxidase. Wilson and coworkers49 claim to have
reduced an Fe(IV) ferryl porphyrin with a Cu( I ) complex to produce an
[ F e ( III) - 0 - C u ( II) ] + product. Its reduced magnetic moment and EPR
silence led them to conclude that the complex was antiferromagnetically
coupled with an S=1 ground state. Chang et a l50 synthesized a
binucleating porphyrin ligand that contained a thiazole sulphide strap
(Figure 1-8). Reactions with Fe( I I I ) and Cu( I I ) produced a compound
which showed a peak at 880cm'l in the IR spectrum (indicating an M-O-M
center) and whose magnetic behavior was f i t to a coupled S=5/2 and
|S =l/2 dimer with -3J=132cm"l. In both cases incomplete
!characterization, especially the lack of x-ray structures, leaves some
j
iquestion about the interpretation of the results.
\ Figure 1-8. Schematic drawing of the thiazole strapped porphyrin
1 synthesized by Chang and co-workers. Reproduced from reference 50. j
!
I
! i
|Sul fur Bridge j
i j
j Based exclusively on EXAFS results, Powers and Chance20 have-
i
|suggested that the bridge coupling iron and copper in cytochrome c
i
i
Joxidase was a sulfur atom from a cysteine residue of the protein.j
jletranuclear iron sulfur clusters51 have shown strong antiferromagneticj
Icoupling (-J>200cm‘ ^) and the crystal structure52 of a binuclear Cu(II)!
I
|complex establishes the v ia b ility of a th iolate bridge. Heteronuclear
j
|model compounds containing sulfur bridged metals have been synthesizedj
| by E llio tt and coworkers. 53" 55 The bis-iron porphyrin copper "trip le -j
I ■ 1
(decker" complexes consist of intermediate spin F e ( III) and C u (II). Thej
jlack of an EPR signal is explained by a combination of dipolar coupling
land weak exchange coupling between the iron and copper which broadens
I the signals to such an extent that they become unobservable. The
istructure of a binuclear Fe/Cu anion has also been determined56 by x-
!
!ray crystallography (Figure 1-9). This compound contains the F e (III)-S -
i
;C u (II) moiety postulated in cytochrome c oxidase, but again the
I
[magnetic and spectral data are consistent with weak coupling.
j
I The amino acid sequence of the enzyme from the bacterium Thermus
|thermophilus contradicts the idea of a cysteine sulfur bridge. 57 Only
[one cysteine is present in this enzyme and since i t must be coordinated
|
to Cua, as indicated by EPR data, there are no available cysteine
residues which can participate in bridging cytochrome 33 and Cug.
Furthermore the sequences for human, bovine, mouse, yeast, and bacteria
contain no conserved cysteines in subunit I which is believed to
contain the cytochrome a3/Cug active s it e . 10
5(3)
S(2)
Cu
S(4)
S(l)
N(2)
Fe(1)
N(3)
,0 (1 )
[Figure 1-9. A view of E llio tt's [ Fe(TPP)(THF) ] [Cu(MNT)2 ] ~ anion, where
M NT = c/s-l,2-dicyanoethylene-l,2-dithialato, TPP = tetraphenyl
porphyrin, and THF = tetrahydrofuran. The cation Fe(TPP)(THF)2 is not
[shown. Reproduced from reference 56.
19
|Carboxyl ate Bridge
The proposal for a carboxyl ate bridge has been mentioned on
! several occasions, 17>43 >58 but i t is not a popularly accepted theory.
i
As in the fi-oxo case, hemerythrin sets a biological precedent for a fi-
x
[carboxylato ligand and strong anti ferromagnetic coupling is evident in
j
\
C u(II) dimers. 59 These include carboxylates forming 3-atom bridges and
t
I
|a single atom bridge, 60 in which the metal centers are completely spin
(paired to produce a diamagnetic product. There has been only one
[attempt to produce an Fe( 111)/Cu(II) p-carboxylato mimic for cytochrome
!
jc oxidase. E llio t t61 has reported the reaction of Fe(II)TPP with a
j C u (III) tripeptide complex (Figure 1-10) forming a Fe( 111)/C u(II)
bridged species. They believe that only the carboxylate end of the
jpeptide can serve as bridging ligand between the two metals, however
its in s ta b ility towards oxygen and lig h t has prevented complete
characterization.
Cu
Fe
J Figure 1 - 1 0 . Possible structure of carboxylate bridged
Fe(TPP)Cu(aib^), where aib3 is the tripeptide of a-aminoisobutyric
I acid (from reference 61). The iron and copper could be bridged by
j e ith er oxygen of the carboxylate ligand. ______ ____ _____ ______
! Other Models
j
; There have been a number of attempts to mimic the active site of
j j
s
j cytochrome c oxidase with bridging ligands other than those described
f
| here. Two reports of non-porphyrinic Fe/Cu complexes incorporate
I
| bridging ligands of phenolic oxygen atoms. A bis-copper iron trim er62
j
| exhibits anti ferromagnetic coupling with -J*=63cm"l, while a series63 of
I
j |
Fe/Cu dimers show coupling with -J=50cm-1 . Gunter's64-66 synthesis of
! a tetranicotinamide porphyrin produced a series of Fe/Cu complexes
I
j
| bridged by halide ions (Figure 1-11). These displayed no magnetic
I coupling due to the fact that the suprastructure of the ligand forced
i
I
; the Cu to be in a magnetically noninteracting position. However the
I
| cyanide bridged complex, 67 displaying ferromagnetic coupling between a
low spin F e ( III) and C u (II), is a reasonable model for the cyanide
I Figure 1-11. A view of the tFe(P)-Cl-Cu(N4)] cation from Gunter's
J /neso-a,or,a,a-tetra(o-nicotinamidophenyl) porphyrin. Reproduced from
preference 6 4 . ___________. ________ _____________ ________
21
adduct of cytochrome c oxidase. Hoping to hold the copper atom in a
position conducive to orbital overlap, Gunter et al also produced a
strapped porphyrin, 68 however in this case the iron displayed magnetic
behavior indicating an S=3/2, S=5/2 spin equilibrium.
Alternative Theories
I t should be noted that strong anti ferromagnetic coupling between
the cytochrome 33 and Cug sites has not been proven as the d e fin itive
answer to th e ir EPR silence, and alternative explanations have been
proposed.
One theory suggests cytochrome 33 is an Fe(IV) fe rryl complex69* 70
while Cub Present in its cuprous state. This model would have the
S=2 ground state shown in the magnetic susceptibility measurements,
but i t assumes a redox inactive role for CU3 and Mossbauer studies71
show no Fe(IV) hemes in either the bovine or bacterial enzyme.
Mossbauer results have also been interpreted72 to suggest weak
coupling (J<0.5cm'^) between cytochrome 33 and Cub which could exist in
the absence of any bridge between the two metals.
A third po ssibility is that the Fe ( I I I ) of cytochrome 33 is
present in an intermediate (S=3/2) or an admixed intermediate (S=3/2,
S=5/2) state and that weak coupling54 between the iron and copper
broaden the EPR signals to the extent that they become unobservable.
Our Approach
In spite of innumerable attempts to determine the active site
structure of cytochrome c oxidase, the exact nature of the ligand
environment surrounding cytochrome 33 and CU3 remains unclear,
especially in regards to a bridging ligand. In order to circumvent the
d iffic u ltie s encountered when studying the enzyme it s e lf , the model
compound approach has been used to simplify the situation. The
objective of this approach is to design metal complexes whose
properties mimic those of the native enzyme so that parallels can be
drawn between the two systems. The key to a successful model is to
retain as many s im ila rities to the enzyme as possible. Once the
properties of the model become to diverse, i t is not possible to draw
conclusions about structural, magnetic and spectral s im ila ritie s .
This work addresses the synthesis of models for cytochrome c
oxidase from two viewpoints. The f ir s t is the design of a binucleating
porphyrin ligand, "Pincer Porphyrin", which is capable of chelating two
metals. I t consists of a tetraphenyl porphyrin base with two
benzimidazole arms capable of simultaneously coordinating a single
metal above the porphyrin plane. A detailed synthesis of Pincer
Porphyrin is outlined in Chapter 2. W e have succeeded in
characterizing mono- and bi-nuclear metal compounds with this ligand
system. Chapter 3 describes the x-ray crystal structure of the
mononuclear Cu(PincerP)-3CHC13 as well as characterization of several
bis-copper complexes, [Cu(PincerP)Cu]X, where X = PFg, BF4 , CIO4 , and
O3 SCF3 . Insertion of F e (II) into the porphyrin results in the bis-THF
23
adduct, Fe(PincerP)(THF)2 » and reactions of this complex as well as its
oxidation product, Fe(PincerP)OH, with various Cu( I ) salts is presented
in Chapter 4.
The second approach to mimic the active site of cytochrome c
oxidase is to react metalloporphyrins with metal imidazolate complexes
to form imidazolate bridged products, which include Fe(TPP)(MIm)2,
[Fe(TPP)(MIm)2 ](B11CH12), Mn(TPP)(MIm), and [Fe(C2Cap)(MIm)](B11CH12) ,
where M = Cu or Ni. The magnetic properties of these compounds has
been studied in detail in order to ascertain the v ia b ility of
imidazolate to mediate strong anti-ferromagnetic coupling as postulated
in cytochrome c oxidase. Details of the synthesis and characterization
of this series of compounds is presented in Chapter 5.
References
1. Wikstrom, M.; Krab, K.; Saraste, M. Cytochrome Oxidase,
A Synthesis; Academic: New York, 1981.
2. Malmstrom, B. G. Quart. Rev. Biophys. 1973, 6, 384-431.
3. Malmstrom, B. G. In Metal Ion Activation of Dioxygen;
Spiro, T. G., Ed.; John Wiley & Sons: New York, 1980; Chapter 5.
4. Stryer, L. Biochemistry; W . H. Freeman: San Francisco, 1981;
Chapter 14.
5. Palmer, G. Pure Appl. Chem. 1987, 59, 749-758.
6 . Kadenbach, B. Angew. Chem., Int. Ed. Engl. 1983, 22, 275-283.
7. Buse, G.; Meinecke, L.; Bruch, B. J. Inorg. Biochem. 1985, 23,
149-153.
8 . Deatherage, J. F.; Henderson, R.; Capaldi, R. A. Chem. Scripta
1983, 21, 35-39.
9. Frey, T. G.; Kuhn, L. A.; Leigh,Jr., J. S.; Costello, M. J .;
Chan, S. H. P. J. Inorg. Biochem. 1985, 23, 155-162.
10. Wikstrom, M.; Saraste, M.; P enttila, T. In The Enzymes of
Biological Membranes, 2nd ed.; Martonosi, A. N., Ed.; Plenum:
New York, 1985; V ol.4, Chapter 48.
11. Einarsdottir, 0 .; Caughey, W . S. Bichem. Biophys. Res. Commun.
1985, 129, 840-847.
12. Naqui, A.; Powers, L.; Lundeen, M.; Chance, B. Biophys. J. 1987,
51, 312a.
13. B lair, D. F.; Martin, C. T.; Gelles, J .; Wang, H.; Brudvig, G. W
Stevens, T. H.; Chan, S. I. Chem. Scripta 1983, 21, 43-53.
14. Babcock, G. T.; Vickery, L. E.; Palmer, G. J. Biol. Chem. 1976,
251, 7907-7919.
15. Van Gelder, B. F.; Beinert, H. Biochim. Biophys. Acta 1969, 189,
1-24.
16. Babcock, G. T.; Callahan, P. M.; Ondrias, M. R.; Salmeen, I.
Biochemistry 1981, 20, 959-966.
17. Peisach, J. In Frontiers of Biological Energetics; Dutton, P. L.
Leigh, J r ., J. S.; Scarpa, A., Eds.; Academic: New York, 1978;
Vol 2, pp 873-881.
25
18. Stevens, T. H.; Martin, C. T.; Wang, H.; Brudvig, G. W.;
Scholes, C. P.; Chan, S. I. J. Biol. Chem. 1982, 257, 12105-12113.
19. Scott, R. A.; Schwartz, J. R.; Cramer, S. P. In Biological and
Inorganic Copper Chemistry; Karlin, K. D.; Zubieta, J ., Eds.;
Adenine: New York, 1985; pp 41-52.
20. Powers, L.; Chance, B.; Ching, Y.; A ng iolillo , P. Biophys. J.
1981, 34, 465-498.
21. Steffens, G. C. M.; Biewald, R.; Buse, G. Eur. J. Biochem. 1987,
164, 295-300.
22. Chan, S. I . ; Brocian, D. F.; Brudvig, G. W.; Morse, R. H.;
Stevens, T. H. In Frontiers of Biological Energetics;
Dutton, P. L.; Leigh, J r ., J. S.; Scarpa, A., Eds.; Academic:
New York, 1978; V o l.2, pp 883-888.
23. Brunori, M.; Antonini, G.; Molatesta, F.; S arti, P.; Wilson, M. T.
In Advances in Inorganic Chemistry: Heme Proteins; Eichorn, G. L.;
M a rz illi, L. G., Eds.; Elsevier: New York, 1988; V o l.7, Chapter 3.
24. Palmer, G.; Babcock, G. T.; Vickery, L. E. Proc. Natl. Acad. Sci.
1976, 73, 2206-2210.
25. Tweedle, M. F.; Wilson, L. J.; Garcia-Iniguez, L.; Babcock, G. T.;
Palmer, G. J. Biol. Chem. 1978, 253, 8065-8071.
26. Stevens, T. H.; Chan, S. I. J. Biol. Chem. 1981, 256, 1069-1071.
27. Cline, J .; Reinhammar, B.; Jensen, P.; Venters, R.; Hoffman, B. M.
J. Biol. Chem. 1983, 258, 5124-5128.
28. Li, P. M.; Gelles, J .; Chan, S. I . ; Sullivan, R. J .; Scott, R. A.
Biochemistry 1987, 26, 2091-2095.
29. Richardson, J. S.; Thomas, K. A.; Rubin, B. H.; Richardson, D. C.
Proc. Natl. Acad. Sci. 1975, 72, 1349-1353.
30. Morgenstern-Badarau, I . ; Cocco, D.; Desideri, A.; R o tilio , G.;
Jordanov, J .; Dupre, N. J. Am . Chem. Soc. 1986, 108, 300-302.
31. Kolks, G.; Lippard, S. J. J. Am . Chem. Soc. 1977, 99, 5804-5806.
32. Katz, R. N.; Kolks, G.; Lippard, S. J. Inorg. Chem. 1980, 19,
3845-3847.
33. Haddad, M. S.; Hendrickson, D. N. Inorg. Chem. 1978, 17, 2622-
2630.
26
34. Haddad, M. S.; Duesler, E. N.; Hendrickson, D. N. Inorg. Chem.
1979, 18, 141-148.
35. Landrum, J. T.; Reed, C. A.; Hatano, K.; Scheidt, W . R.
J. Am. Chem. Soc. 1978, 700, 3231-3234.
36. Landrum, J. T.; Grimmett, D.; H aller, K. J .; Scheidt, W . R.;
Reed, C. A. J. Am. Chem. Soc. 1981, 103, 2640-2650.
37. Cutler, A. C.; B ritta in , T .; Boyd, P. D. W . J. Inorg. Biochem.
1985, 24, 199-209.
38. Prosperi, T.; Tomlinson, A. A. G. J. Chem. Soc., Chem. Commun.
1979, 196-197.
39. Saxton, R. J .; Wilson, L. J. J. Chem. Soc., Chem. Commun. 1984,
359-361.
40. Dessens, S. E.; M e rrill, C. L.; Saxton, R. J .; Ila r ia , J r ., R. L.;
Lindsey, J. W.; Wilson, L. J. J. Am. Chem. Soc. 1982, 104, 4357-
4361.
41. Chunplang, V.; Wilson, L. J. J. Chem. Soc., Chem. Commun. 1985,
1761-1763.
42. Reed, C. A.; Landrum, J. T. FEBS Lett. 1979, 106, 265-267.
43. Blumberg, W . E.; Peisach, J. Cytochrome Oxidase; King, T. E.;
O rii, Y.; Chase, B.; Okunuki, K., Eds.; Elsevier: New York, 1979;
pp 153-159.
44. Ingraham, L. L.; Meyer, D. L. Biochemistry of Dioxygen; Plenum:
New York, 1985; Chapters 9 and 10.
45. Murray, K. S. Coord. Chem. Rev. 1974, 12, 1-35.
46. Woodruff, W . H.; Dallinger, R. F.; A ntalis, T. M.; Palmer, G.
Biochemistry 1981, 20, 1332-1338.
47. Shaw, R. W.; Rife, J. E.; O'Leary, M. H.; Beinert, H.
J. Biol. Chem. 1981, 256, 1105-1107.
48. Armstrong, F.; Shaw, R. W.; Beinert, H. Biochim. Biophys. Acta
1983, 722, 61-71.
49. Saxton, R. J .; Olson, L. W.; Wilson, L. J. J. Chem. Soc., Chem.
Commun. 1982, 984-986.
50. Chang, C. K.; Koo, M. S.; Ward, B. J. Chem. Soc., Chem. Commun.
1982, 716-719.
51. Laskowski, E. J .; Frandel, R. B.; Gillum, W . 0 .;
Papaefthymiou, G. C.; Renaud, J .; Ibers, J. A.; Holm, R. H.
J. Am . Chem. Soc. 1978, 100, 5322-5337.
52. Aoi, N.; Takano, Y.; Ogino, H.; Matsubayashi, G.; Tanaka, T.
J. Chem. Soc., Chem. Commun. 1985, 703-704.
53. E llio t t, C. M.; Akabori, K. J. Am . Chem. Soc. 1982, 104, 2671-
2674.
54. Schauer, C. K.; Akabori, K.; E llio t t, C. M.; Anderson, 0. P.
J. Am. Chem. Soc. 1984, 106, 1127-1128.
55. H atfield, W . E.; E llio t t , C. M.; Ensling, J .; Akabori, K.
Inorg. Chem. 1987, 26, 1930-1933.
56. Serr, B. R.; Headford, C. E. L.; E llio t t, C. M.; Anderson, 0. P.
J. Chem. Soc., Chem. Commun. 1988, 92-94.
57. Zimmerman, B. H.; Nitsche, C. I . ; Fee, J. A.; Rusnak, F.;
Munck, E. Proc. Natl. Acad. Sci. 1988,
58. Seiter, C. H. A.; Angelos, J r ., S. G.; Perrault, R. A.
In Frontiers of Biological Energetics; Dutton, P. L.;
Leigh, J r ., J. S.; Scarpa, A., Eds.; Academic: New York, 1978;
Vol. 2, pp 897-903.
59. Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry,
3rd ed.; Interscience: New York, 1972; pp 918-920.
60. Davis, A. R.; Einstein, F. W . B.; Curtis, N. F.; Mattin, J. W . L.
J. Am. Chem. Soc. 1978, 100, 6258-6260.
61. E llio t t, C. M.; Jain, N. C.; Cranmer, B. K.; Hamburg, A. W .
Inorg. Chem. 1987, 26, 3655-3659.
62. Morgenstern-Badarau, I . ; Wickman, H. H. Inorg. Chem. 1985, 24,
1889-1892.
63. Okawa, H.; Kanda, W.; Kida, S. Chem. Letts. 1980, 1281-1284.
64. Buckingham, D. A.; Gunter, M. J .; Mander, L. N. J. Am. Chem. Soc.
1978, 100, 2899-2901.
65. Gunter, M. J .; Mander, L. N.; McLaughlin, G. M.; Murray, K. S.;
Berry, K. J .; Clark, P. E.; Buckinghan, D. A. J. Am. Chem. Soc.
1980, 102, 1470-1473.
6 6 . Berry, K. J .; Clark, P. E.; Gunter, M. J .; Murray, K. S.
Nouv. J. Chim. 1980, 4, 581-585.
28
67. Gunter, M. J .; Berry, K. J .; Murray, K. S. J. Am. Chem. Soc. 1984,
106, 4227-4235.
6 8 . Gunter, M. J .; Mander, L. N.; Murray, K. S.; Clark, P. E.
J. Am. Chem. Soc. 1981, 103, 6784-6787.
69. Seiter, C. H. A.; Angelos, S. G. Proc. Natl. Acad. Sci. 1980, 77,
1806-1808.
70. Hagen, W . R. Biochim. Biophys. Acta 1982, 702, 82-98.
71. Kent, T. A.; Young, L. J .; Palmer, G.; Fee, J. A.; Munck, E.
J. Biol. Chem. 1983, 258, 8543-8546.
72. Rusnak, F. M.; Munck, E.; Nitsche, C. I . ; Zimmerman, B. H.;
Fee, J. A. J. Biol. Chem. 1987, 262, 16328-16332.
29
Chapter 2
Pincer Porphyrin
Numerous enzymes from biological systems contain one or more
metals in th e ir active sites. Iron, copper, cobalt, manganese, and zinc
are the most commonly found metal elements, 1 and many of these
metallobiomolecules have been studied using the model compound
approach. This method centers around the idea that small synthetic
molecules can duplicate the active site of proteins and afford valuable
information regarding structure and mechanism. These synthetic
analogues consist of re la tiv e ly low molecular weight metal complexes
which do not contain the bulky protein conformation which is often the
cause of d iffic u lty in studying the native proteins. This biomimetic
approach has been proven as a successful method in gaining structural
and mechanistic details relating to metalloproteins.
Included in the long l i s t of metalloproteins studied by this
method are the oxygen carriers, myoglobin, hemoglobin, hemocyanin, and
hemerythrin; the electron transport proteins, cytochrome c, the blue
30
copper proteins, and iron-sulfur proteins; as well as cytochrome P450,
nitrogenase, and cytochrome c oxidase. The approach has been
particularly successful in studying the oxygen binding of myoglobin and
hemoglobin as in Collman's picket fence porphyrins2 and Baldwin's
capped porphyrins. 3 Synthetic analogues of the iron-sulfur proteins4
have also been obtained as well as cytochrome c models. 5’ 6 An
important aspect of the success of these models has been d e fin itiv e
structural characterization in the form of x-ray crystal structures.
Without this knowledge, i t is exceedingly d if f ic u lt to draw meaningful
comparisons between model compounds and the native enzymes. This is
due in part to the intimate relationship between the structure and
mechanism of metalloproteins. Attempts to mimic the active site of
cytochrome c oxidase have been sorely lacking in complete structural
characterization. The work by other groups discussed in Chapter 1
resulted in very few x-ray crystal structures, and from the very
beginning of this project, our ultimate goal was d e fin itiv e structural
characterization of a cytochrome c oxidase model.
Ligand Design Strategy
In order to mimic the active site of cytochrome c oxidase, we have
designed a lig a n d system c o n s is tin g o f a d e riv a tiz e d
tetraphenylporphyrin. The name "pincer porphyrin" was chosen because
of the s im ila rity between the benzimidazole arms which coordinate a
second metal above the porphyrin plane and the pincers on a crab. A
schematic drawing of pincer porphyrin is shown in Figure 2-1. I t
consists of a tetraarylporphyrin in which two phenyl rings trans to
o c
CO
HN
NH
HN
CO
NH
Figure 2-1. Schematic drawing of pincer porphyrin, a binucleating ligand capable of
holding two metals in close proximity.
32
each other are connected to benzimidazole rings via an amide linkage.
The remaining trans phenyl rings support pivalamide groups as in the
fa m iliar picket fence porphyrin.
There are several key design features which were incorporated into
the ligand in the hope that a successful model of cytochrome c oxidase
would be achieved. First of a ll, i t is a binucleating porphyrin
capable of holding two metals in close proximity. Although the
porphyrin base lacks the exact side groups found in heme a, an iron
placed in the porphyrin ring w ill exhibit the characteristic spin state
and structural properties as the iron found in cytochrome 33 of
cytochrome c oxidase. The second binding site is reserved for copper
and consists of two benzimidazole ligands. The fact that these
benzimidazoles are trans to each other w ill force the "upstairs" copper
to lie d ire c tly over the iron in the porphyrin ring.
Secondly, difunctionalization of the phenyl groups rather than
tetrafunctionalization w ill keep the upstairs metal from becoming
trapped in a magnetically noninteracting position. Gunter and
coworkers7 observed that in the tetranicotinamide porphyrin, the
tetracoordinate copper directed its magnetic orbital (dx2 -y2) away
from the iron d-orbitals and therefore overlap was prohibited.
Difunctionalized porphyrins have been synthesized previously8" 10 in the
form of diphenyl rather than tetraphenyl porphyrins, so that further
derivatization is not possible. An exception is the basket handle
porphyrin11 which contains straps on either side of the porphyrin ring
connected to trans phenyl rings.
33
Thirdly, the pivalamido groups, or pickets, play an important role
in th a t they serve to isolate the "active site" of the
metalloporphyrin. By s te ric a lly blocking the metal sites, the pickets
w ill help avoid complicated intermolecular interactions. These
functional groups also make the molecule block-shaped overall which
w ill aid in crystallizatio n and th e ir presence w ill increase the
organic solvent so lu b ility of the molecule.
Fourthly, the benzimidazoles are attached to the phenyl rings via
an amide functional group and one methylene group. The re la tiv e ly
short length of this attachment should ensure that no in tra - or in te r
molecular interactions occur between the benzimidazoles and the iron
porphyrin. W e have also chosen the 2-methyl derivative of
benzimidazole again to avoid coordination of the nitrogen lone pair to
iron in the porphyrin ring. I t has been shown previously that this 2-
methyl group on imidazole provides adequate steric hindrance to block
six-coordination of ferrous porphyrins. 12
F ifth ly , the methylene group of the benzimidazole arms should help
give some f le x ib ilit y to the ligand in order to have working
s o lu b ility , and yet s t i l l retain enough r ig id ity to c ry s ta llize w ell.
This is an extremely important tradeoff in attempts to grow crystals of
metalloporphyrins. I f too rig id , the compounds become insoluble in
organic solvents, while i f too fle x ib le , they w ill not pack e ffic ie n tly
in the crystal la ttic e and x-ray quality crystals may be unobtainable.
The final design feature of pincer porphyrin is the a b ility to
incorporate various exogenous bridging ligands between the two metal
sites. This w ill allow studies correlating bridging ligand and extent
34
of magnetic coupling, which is an important aspect of modelling
cytochrome c oxidase in view of the uncertainty regarding its bridging
1 igand.
Synthesis of Pincer Porphyrin
Derivatized porphyrins are notorious for th e ir long and tedious
synthesis, and pincer porphyrin is no exception. The synthesis begins
with the previously reported13’ 14 a,a,a,a-tetra(o-aminophenyl)porphyrin
(abbreviated four-up amino). Due to the atropisomerism15 of the phenyl
rings, there exist four differen t isomers in a s ta tis tic a l mixture, and
the desired isomer, "four-up", is present as 12.5% of the total (Figure
2-2). However, the four-up amino can be enriched by refluxing a
toluene solution of the mixture in the presence of s ilic a g e l. 16’ 17
Since four-up amino has the highest polarity of the isomers, i t binds
most strongly to the s ilic a gel. At reflux temperature, isomeric
equilibrium allows a build-up of the most strongly adsorbed component
until most of the tetraaminophenyl porphyrin is bound to the s ilic a gel
as four-up amino. I t can then be cooled and removed from the s ilic a
gel via column chromatography to separate any of the unwanted isomers.
I f purified four-up amino is treated with excess pivaloyl
chloride, the product is the tetrasubstituted picket fence porphyrin, 14
but i f 2 equivalents of pivaloyl chloride are used, five products are
formed: te tra -, t r i - , cis- and trans-di-, and mono-picketporphyrin.
The d e sirab le tra n s -d ip ic k e t (form ally named a,a ,5 ,1 5-b is (o -
aminophenyl) - a ,a ,10 , 20 -bis(pivalamidophenyl) porphyrin, but referred to
as tra/?s-dipicket) is among the reaction products, but three problems
12.5% a,a,a,a
four up amino
NHg
NH,
N H ,'
N ^
25% a,a,P,P
U
NH, ^
N H ,
N H ,
50% a,a,a,P
1 1
I^H ,
C
N H ^ ^ N H ,
12.5% a,p,a,p
Figure 2-2. Statistical mixture of the four atropisomers of tetra(o-aminophenyl)porphyrin.
U )
c n
!make this direct acylation route impractical. (1) The t-butyl group iSj
not bulky enough to in hibit te tra - or t r i - functionalization nor to 1
favor trans- over cis- difunctionalization. (2) The c/s-dipicket isl
i
(s ta tis tic a lly favored 2:1 over desired trans-dipicket. (3) The c /s- 1
j and trans-dipicket are chromatographically inseparable by conventional!
1 1
imeans.
I !
I
' In order to circumvent these problems, we use a t r it y l protecting]
! I
group which is bulky enough to in h ib it te tra - and tri-products, andi
l
i |
jwhich favors the trans- over the c/s-diproduct. The triphenylmethyl]
group has been found18 to be a convenient protecting group for'
i
jtetraaminophenyl porphyrins and can be easily removed by treatment
'with acid. Four-up amino is treated with two equivalents!
j , !
. tritylbrom ide resulting in four products (Figure 2 -3). The te tr a tr ity l
j j
product is avoided completely. In this case the trans-di- and the t r i -
i ;
j t r i t y l move at the same rate on the chromatography column, but,
I separation is possible after treatment with pivaloyl chloride followed:
iby acid cleavage of the t r it y l protecting group.
I ;
i Another advantage of the t r it y l method over direct acylation is;
that the unneeded mono- and c /s -d i- products can be recycled back to!
i
; four-up amino by acid cleavage of the t r it y l groups thereby milking the
l
| reaction fo r additional y ie ld . The overall yield of trans-dipicket
; from four-up amino is 25%, and the use of the bulky t r it y l group'
r
; results in a 3-fold enhancement of the trans product over the cis.
j An improved synthesis includes using an even bulkier protecting
I
jgroup, 4 , 4 ' , 4 " -tris(benzoyloxy)tritylbrom ide. This extremely large
i
! protecting group was in it ia lly used to block nucleoside hydroxyl or
PhjCBr
four up amino -------------- )
CPfu
9 R V NFL 9 p*h NH
N H L ^ m . ---------
^ 1) (C H ^C C O C I
2 ) OjCCOOH
trans-dipicket
Figure 2-3. Reaction of four up amino with tr ity l bromide to form the mono-, c /s -d i-, trans-di-,
and t r i - t r i t y l products. The ring represents tetraphenyl porphyrin. Pivaloyl chloride is then
added to a mixture of trans-di- and t r i - t r i t y l followed by acid cleavage of the tr ity l protecting
group to leave monopicket and the desired trans-dipicket.
38
amino groups. 19’ 20 Treatment of four-up amino with th is reagent
results again in four products; t r i t r i t y l , c/s-and t r a n s -d itr ity l, and
monotrityl, but the t r i - and mono-trityl are minor components and the
yield of tra n s -d itrity l in this reaction is 45% (Figure 2-4). The
pickets again are added using pivaloyl chloride and base is used to
cleave the benzoyloxytrityl protecting group.
The benzimidazole moieties consist of 2,5,6-trimethylbenzimid-
azole. This substituted benzimidazole has been prepared previously, 21
but we have modified the synthesis to produce higher yields. The
formation of the 2 -acetate derivative and conversion of this to its
acid chloride is necessary before condensation with the porphyrin
phenyl amines of trans-dipicket (Figure 2-5).
Characterization
The absorption spectrum of pincer porphyrin in chloroform shows a
Soret band at 423nm and four additional bands at 517, 550, 592, and
647nm which is typical of unmetallated porphyrins. 22 Elemental
analysis of the porphyrin is consistent with our predicted model and
shows the presence of one water molecule per porphyrin regardless of
extensive drying methods. FAB-MS was conducted on the free porphyrin
showing the parent (M+H)+ ion at 1243.
The *H N M R in CDCI3 gives some information regarding the
conformation of the ligand superstructure (Figure 2-6). The pyrrole
protons which appear as a singlet in unsubstituted or in te tra -
substituted phenyl porphyrins are now s p lit into a doublet of
doublets. This is due to the lowering of symmetry to C2V* This AB
TBTrBr =
four up amino
C -O CBr
TBTr
N H _
TBTr NH, TBTr
C j * J
H TBTr
TBTr
TBTr NH
p . —
C j " * J
y
C H g C o a
pincer porphyrin f
1) (CHj X jCCOCI
2) NaOH
trans -dipicket
Figure 2-4. Reaction of four up amino with 4 ,4 ',4"-tris(benzoyloxy)trityl bromide results in
minor fractions of the mono- and t r i - t r i t y l products, as well as the cis~ and tra n s -d itrity l.
The pickets are added using pivaloyl chloride and base is used to cleave the tr ity l protecting
group, frans-dipicket is combined with the benzimidazole acid chloride to form pincer porphyrin.
XX
C H jC0 2H
NaOH
C ^ C X )2CH3
SOO*
CHjCX^H
CHgCOj CI
Figure 2-5. Acetic acid and 4,5-o-phenylenediamine are condensed to form 2,5,6-trimethyl -
benzimidazole. This is alkalated using bromomethyl acetate, and base converts the ester to the
acid. Reaction with thionyl chloride forms the acid chloride which is then mixed with tran s
dipicket to form pincer porphyrin.
41
type pattern has been observed for the pyrrole protons in Momenteau's
"hanging base" porphyrins. 23 Sim ilarly, s p littin g of the pyrrole
resonance of tetraphenyl porphyrin occurs when the tautomerism2 4 * 25 of
the center protons is slowed down s u ffic ie n tly by lowering the
temperature to -80°C (Figure 2-7).
The 2-methyl group on the benzimidazole is shifted upfield to
-1.70ppm whereas the resonance of the same group on 2,5,6-trim ethyl -
benzimidazole acetic acid occurs at 2.75ppm. This indicates that the
methyl group is experiencing ring current s h ift from the aromatic
porphyrin and therefore lie s over the top of the porphyrin ring rather
than at the periphery where a downfield s h ift would occur. The methyl
groups at the 5 and 6 positions of the benzimidazole do not experience
any downfield s h ift due to ring current. This is seen by comparing the
resonance of pincer porphyrin (6 2.28 and 2.36) to starting material (5
2.32).
W e suspect that each benzimidazole moiety is held in this position
by hydrogen bonding between its nitrogen lone pair and the amide group
on the adjacent picket. This is supported by a downfield s h ift of
these picket amides (69.79) which is consistent with hydrogen bonding.
A 2ppm downfield sh ift has been observed for amide protons of a
tetrasubstituted phenyl porphyrin where hydrogen bonding occurs
between the amides and coordinated dioxygen. 26 Further evidence is
presented in the x-ray crystal structure of the mononuclear copper
9 7 8 6 5 1 0 3 2 / 0 -2 -3
Figure 2-6. 90MHz N M R of pincer porphyrin in CDC1 3 .
43
I i
- complex in the following chapter. For the free porphyrin in solution
we know this H-bonding is not static since the resonance fo r the
methylene protons appear as a singlet (63.91). This indicates that
rotation about this carbon is occurring and the benzimidazole moieties
, are "flipping" and alternately hydrogen bonding to f ir s t one picket
I amide and then the other.
Figure 2-7. Tautomerism of the central porphyrin protons.
44)
!
Experimental j
i
Solvent purification was performed as follows: Dichloromethane!
j j
•was dried over 4A molecular sieves. Pyridine was dried over K0H,i
I !
d is tille d under nitrogen, and stored over 5A molecular sieves. Benzenei
jand heptane were d is tille d from sodium/benzophenone. Thionyl chloridej
! was d is tille d from triphenylphosphite and stored under nitrogen. A11!
t ;
I other solvents were used without pu rification . Column grade s ilic a gel;
! I
! was EM(Merck) 100, 70-230 mesh and pic grade s ilic a gel was 60 PF254;
i ;
: (Merck7747). Thin layer chromatography was performed on Analtech
1 S ilic a Gel G F plates. N M R spectra were recorded on IBM WP270-SY or'
\ !
;JE0L FX-90Q instruments. Absorption spectra were obtained on a!
i !
i Shimadzu UV260 spectrophotometer. Elemental analyses were performed at
the University of C alifornia, Berkeley, Microanalytical Laboratory and
I
FAB mass spectra were performed at the Mass Spectrometry F a c ility ,'
i ^
I University of C alifornia, San Francisco.
(
I !
t Trans-dipicket via the triphenvlmethvl bromide protecting group ;
i a,g,Q!,Q!-/neso-tetra(o-aminophenyl)porphyrin (3.84g, 5.69mmol) was
|
dissolved in dichloromethane (150mL) and pyridine (3mL). Anhydrous(
i
j K2CO3 (3.2g, 23mmol) was added and the solution was cooled to 0°C and
I flushed with nitrogen. A solution of triphenylmethyl bromide (3.67g,
1
:11.4mmol) in dichloromethane (lOOmL) was added dropwise over a period
! of lh r and the solution was stirred for an additional 30min. )
The reaction mixture was washed with 10% aqueous NaCl (lOOmL), 10%
jaqueous NH4O H (lOOmL), and again 10% aqueous NaCl (4X100mL), then dried
iwith anhydrous Na2S0 4 . The solvent was removed and the residue was
45
dissolved in dichloromethane (75mL) and adsorbed onto S ilic a Gel 100
(50mL). The solvent was again removed and the product/silica gel
mixture was dried under vacuum for 2hrs. I t was then carefully loaded
on a S ilic a Gel 100 column (12 X 50cm, heptane packed) as a heptane
slurry, and fresh s ilic a gel and sand were loaded above to prevent back
d iffu s io n . E lu tion with 9:1 hexanes/ethyl acetate then 7:3
hexanes/ethyl acetate produced three major bands, whose solvents were
removed. The f ir s t band was a mixture of t r it y l and trans- d it r it y l
(3g, Rf0.69, 7:3 hexanes/ethyl acetate). The second band was cis-
d it r it y l ( 2 .lg , 32%, Rf0.47, 7:3 hexanes/ethyl acetate). The th ird band
was the previously reported m onotrityl. 17 Continued elution with 1:1
acetone/diethyl ether collected any unreacted four-up amino.
The t r it y l and trans- d it r it y l mixture (l.Og) was dissolved in
dichloromethane (lOOmL) and pyridine (0.6mL) and cooled to 0°C under
nitrogen. A solution of pivaloyl chloride (lmL, 8.1mmol) in
dichloromethane (20mL) was added dropwise over 5min and the solution
was stirred 3hrs. The reaction mixture was washed with lOOmL each of
10% aqueous NaCl, 10% aqueous NH4OH, 10% aqueous NaCl, IN HC1, 10%
aqueous NaCl, 10% aqueous NH4OH, and fin a lly twice with 10% aqueous
NaCl. The solution was dried with anhydrous Na2S04 and the solvent
removed.
The residue was dissolved in dichloromethane (30mL) and cooled to
0°C under nitrogen. A solution of trichloroacetic acid (1.58g,
9.67mmol) in dichloromethane (20mL) was added and the mixture was
stirred for 2hrs. I t was then washed with 10% aqueous NH4O H (lOOmL),
I 46!
t I
iand 10% aqueous NaCl (lOOmL), dried with anhydrous Na2S0 4 , and the;
solvent removed. j
The products were dissolved in dichloromethane (30mL) and adsorbed,
; onto pic grade s ilic a gel (lOmL). The solvent was removed and the
! mixture was dried under vacuum for 2hrs. I t was then loaded on a p lc:
I
jgrade s ilic a gel column (5 X 7cm, packed with heptane) and eluted with
6:1 chloroform/diethyl ether. Two major bands were collected, the
i '
j f ir s t being the previously reported monopicket. 17 The second band was,
the desired trans-dipicket (0.39g, 24% from four-up amino). Rf0.42, 3%
i
methanol/chloroform. l H N M R (270 MHz, CDC13) 6 -2.64 (s, 2H), 0.28 (s,
18H), 3.54 (s,4H ), 7.1-8.0 (m, 16H), 8.71 (d, 2H, J=8 . 6Hz), 8.79 (d,
4H, J=4.9Hz), 8.9 (d, 4H, J=4.8Hz). Anal. Calcd. for C s ^ s q N ^ ^ O :
C,75.32; H,6.09; N,13.04. Found: C,75.08; H,5.77; N,13.08.
T ra n s -d ip ic k e t via the 4 .4 ' .4 " -tris (b e n z o v lo x v )tritv l bromide
protecting group.
4 ,4 7 , 4 ' ' -T ris (b e n zo ylo x y )trity l bromide was available from
Aldrich, but needed to be recrystallized to remove im purities. Hot
benzene (40mL) was used to dissolve 5g of m aterial. The dark orange
1 impurities were removed by filtr a tio n and the solution was allowed to
cool. Heptane (20mL) was slowly added to the cloudpoint. Peach
crystals formed overnight and were filte re d and rinsed with 2:1
heptane/benzene (60mL) and with heptane (20mL). The product was dried
under vacuum and stored in the dark.
a,a,a,a-A/eso-tetra(o-aminophenyl)porphyrin (0.56g, 0.83mmol) was
dissolved in dichloromethane (120mL) and cooled to 0°C under nitrogen.
I
47j
K2CO3 (0.23g, 1.66mmol), pyridine (2mL), and 4 , 4 ' , 4 ' ' -tris(benzoyloxy)- 1
i
t r it y l bromide (1.74g, 2.55mmol, 3.07eqs) were added. The reaction;
mixture was stirred 2 hrs and checked for completion by tic in!
j
dichloromethane. ( I f there was a substantial amount of unreacted;
four-up amino which stayed at the origin, or of the monotritylated'
product (Rf0.06), more t r i t y l bromide was added in small quantities.!
I
; Note that i f too much was added the amount of t r i t r i t y l product'
< i
i (Rf0.34) increased.) Workup of the reaction mixture consisted ofi
! i
|washing with lOOmL each of IN H C 1 (2X), 10% NH4O H (2X), and 10% aqueousj
|NaCl (2X). The dichloromethane solution was then dried with anhydrous'
; Na2S04 and the solvent removed. The products were dissolved in 8:2
idichloromethane/hexanes and loaded on a 3.5 X 19cm column of pic grade
s ilic a gel packed with 8:2 dichloromethane/hexanes. Elution with the
I
same solvent afforded two major and two minor bands. The fastest!
moving fraction was the desired trans-d itris(b en zo ylo x y)trityl (0 . 68g,
43%). Rf0.44, dichloromethane. Anal. Calcd. for
‘ C124H86N8°1 2*°-5CH2C12 : c > 77.77; H, 4.57; N, 5.83. Found: C, 77.56;
r
\ H, 4.63; N, 5.53. FAB-MS: (M+H)+ 1879. JH N M R (270MHz, CDCI3 ) 8 -2.52;
(s, 2H), 3.58 (s, 4H), 5.50 (s, 2H), 6 .8 -8 .2 (m, 70H), 8.93 (d, 4H,
|J=4.9Hz), 8.98 (d, 4H, J=4.9Hz).
! Continued elution with dichloromethane afforded the second major
band which was the c f s - d it r it y l. Rf0.19, dichloromethane. Anal. Calcd.
for C124H86N8012-CH2Cl2: C, 76.40; H, 4.47; N, 5.70. Found: C, 76.69;
H, 4.55; N, 5.73. FAB-MS: (M+H)+ 1879. *H N M R (270MHz, CDC13) 8 -2.58
(s, 2H), 3.55 (s, 4H), 5.30 (s, 2H), 6 .8-8.0 (m, 70H), 8.89 (s, 2H),
8.91 (d, 2H, J=5.4Hz), 8.95 (d, 2H, J=5.4Hz), 9.06 ( s , 2 H ) .
48
The two minor fractions at Rf0.27 and Rf0.04 were the t r i - and
mono-trityl products, respectively. T r it r it y l: FAB-MS: M + 2483. *H
N M R (270MHz, CDC13) S -2.49 (s, 2H), 3.45 (s, 2H), 5.60 (s,3H), 6.80-
8.25 (m, 98H), 8.91-9.10 (m,8 H). Monotrityl: N M R (270MHz CDC13)
d -2.68 (s, 2H), 3.55 (s, 6H ), 5.20 (s, 1H), 6 .8 -8 .1 (m, 43H), 8.87-
8.98 (m, 8 H).
7rans-ditris(benzoyloxy)trityl (1.85g, 0.98mmol) was dissolved in
dichloromethane (120mL) and pyridine (2mL). The solution was cooled
to 0°C and flushed with nitrogen. Pivaloyl chloride (1.5mL, 12.2mmol)
was added and the solution was stirred for 4hrs. I t was then washed
with IN H C 1 (2 X lOOmL), 10% aqueous NH4O H (2 X lOOmL), and 10% aqueous
NaCl (3 X lOOmL). The resulting dichloromethane solution was dried
with anhydrous Na2S04 and the solvent removed.
The residue was dissolved in tetrahydrofuran (lOOmL) and ethanol
(15ml_). Aqueous NaOH (20mL, 1M) was added and the solution stirred for
90min. I t was then neutralized with IN H C 1 and dichloromethane
(200mL) was added. At least 7 times the deep red solution was washed
with water (150mL). The dichloromethane solution was then dried with
anhydrous Na2S04 and the solvent removed.
The product was purified on a 3.5 X 19cm pic grade s ilic a gel
column loaded with 6:1 chloroform/hexanes. The major band was the
desired trans-dipicket (61g, 74%).
49
2 ,5 ,6 - trimethylbenzimidazole
A solution of 4,5-dimethyl-o-phenylenediamine (2 7 .2g, 0.20mmol) in
4N H C 1 (250mL) was heated until all solid was dissolved. Glacial
acetic acid (18mL) was added and the solution refluxed fo r 24hrs. As
i t was allowed to cool slowly, a lig h t brown solid formed and after
further cooling in an ice bath, i t was filte re d and rinsed with 4N
NH4O H (200mL). The solid was dried under vacuum overnight then
dissolved in hot 1:2 chloroform/methanol (lOOmL) and allowed to
c ry s ta llize upon cooling. The tan crystals were filte re d and the f ir s t
crop yielded 16.3g, 51%, while the second crop yielded 10.Og, 31%.
N M R (90 MHz, CD3OD) 8 2.32 (s, 6H), 2.50 (s, 3H), 7.21 (s, 2H).
2 -TN-(2 .5 .6 -trimethvlbenzimidazolvl)1 acetate
To a slurry of dewaxed NaH (1.80g, 75mmol) in dry tetrahydrofuran
(lOOmL) under nitrogen, the 2,5,6-trimethylbenzimidazole (10.Og,
62mmol) was added and stirred 2hrs. A solution of methyl-2-
bromoacetate (6 .8mL, 71.8mmol) in tetrahydrofuran (lOmL) was added over
lOmin and the solution refluxed for 24hrs. I t was then cooled and
chloroform (lOOmL) was added. The NaBr was filte re d o ff and the
solvent removed under vacuum. The residue was redissolved in a
minimum amount of hot methanol and diethyl ether was added dropwise to
the cloudpoint. The solution was refrigerated and the resulting white
crystals were filte re d and rinsed with diethyl ether. (7.02g, 49%)
N M R (90MHz, CDCI3 ) 5 2.35 (s, 6H), 2.52 (s, 3H), 3.75 (s, 3H), 4.76 (s,
2H), 6.94 (s, 1H), 7.43 (s, 1H).
50
2-rN-(2,5,6-trimethy1benzimidazovl11acetic acid
The corresponding ester (5.63g, 24mmol) was suspended in d is tille d
water (lOOmL) and NaOH (l.O g, 25mmol) was added. The slurry was
stirred until all solid dissolved (2hrs). The pale yellow solution was
reduced to half the volume and upon neutralization with IN HC1 a white
solid formed. This was filte re d and rinsed with d is tille d water and
dried under vacuum overnight. (5.04g, 96%) Anal. Calcd. for CJ2N14N2O:
C, 66.03; H, 6.48; N, 12.84. Found: C, 65.84; H, 6.43; N, 12.69.
! H N M R (90MHz, CD3OD) S 2.43 (s ,6H), 2.75 (s,3H), 4.90 (s, 2H), 7.44
(s,1H ), 7.48 (s, 1H).
Qr,g,5.15-bisrN-(2, 5. 6- t r i methyl benzimidazol v l ) acetamidophenvl 1 -
a,Q!,10.20-bis(pivalamidophenyl )porphine, Pincer Porphyrin
The 2 - [N -(2 , 5 , 6 - trimethylbenzimidazoyl) ]acetyl chloride was
prepared in situ. To a slurry of 2-[N -(2,5,6-trim ethylbenz-
im idazoyl)]acetic acid (0.25g, 1.15mmol) in dichloromethane (25mL) was
added thionyl chloride (0.085mL, 1.17mmol) and dimethylformamide
(lmL). The slurry was stirred overnight producing a pale orange
solution which was then cooled to 0°C and flushed with nitrogen.
7Vans-dipicket (0.103g, 0.122mmol) was added. Approximately lmL of
pyridine was added dropwise until the solution color changed from dark
green to red. The reaction mixture was stirred for 2hrs. Workup of
the reaction consisted of washing with lOOmL each 10% NH4OH, 10%
aqueous NaCl, IN HC1, 10% aqueous NaCl, 10% NH4OH, and fin a lly twice
with 10% aqueous NaCl. The resulting dichloromethane solution was
dried with anhydrous Na2S0 4 , and solvent was evaporated. The product
51
was purified on a 2 X 10cm column of pic grade s ilic a gel eluting with
4:3:3 dichloromethane/diethyl ether/hexanes. The desired major
fraction was preceded by some minor components. C rystallization from
dichloromethane/pentane gave dark purple crystals (0.15g, 98%).
Rf0.22, 4:3:3 dichloromethane/diethyl ether/hexanes. Anal. Calcd. for
C78H74N12^4 *H2O; C, 74.25; H, 6.08; N, 13.32. Found: C, 74.54; H, 5.83;
N, 13.21. FAB-MS: (M+H)+ 1243. l H N M R (270MHz, CDCI3 ) S -2.70 (s,
2H), -1.70 (s, 6 H), 0.25 (s, 18H), 2.28 (s, 6H), 2.36 (s, 6 H), 3.91 (s,
4H), 6 .9-8.7 (m, 30H), 9.79 (s, 2H).
Special acknowledgment of previous work on the synthesis of pincer
porphyrin is due to Dr. Nigel G. Larsen, Dr. Brian S. Erler, Dr. John
R. Tate, and Susan Rasmussen. Also, preliminary reactions with the
tris(b en zoyloxy)trityl protecting group were performed by Dr. Steven J.
Rodgers and Anthony Watson.
Summary
W e have succeeded in designing and synthesizing a p o tentially
binucleating ligand, pincer porphyrin, whose metal complexes may serve
as cytochrome c oxidase models. Important features were incorporated
into the ligand to achieve this goal. Our synthesis is the f ir s t
successful trans di functional ization of an a,o:,a,a-orthosubstituted
tetraaryl porphyrin, and i t was accomplished with the use of bulky
protecting groups (either triphenylmethyl or 4 , 4 ' , 4 ' ' -tris(b e n zo yl-
o x y )trity l). A thorough characterization of pincer porphyrin both in
solution and as a solid has been carried out.
References
- 1. Ibers, J. A.; Holm, R. H. Science, 1980, 209, 223-235.
! 2. Collman, J. P. Acc. Chem. Res. 1977, 10, 265-272.
1 3. Hashimoto, T .; Dyer, R. L.; Crossley, M. J .; Baldwin, J. E.;
j Basolo, F. J. Am. Chem. Soc. 1982, 104, 2101-2109.
4. Holm, R. H. Acc. Chem. Res. 1977, 10, 427-434.
5. Mashiko, T.; Marchon, J. C.; Musser, D. T .; Reed, C. A.; Kastner,
M. E.; Scheidt, W . R. J. Am. Chem. Soc. 1979, 101, 3653-3655.
6 . Mashiko, T.; Reed, C. A.; H aller, K. J .; Kastner, M. E.;
Scheidt, W . R. J. Am. Chem. Soc. 1981, 103, 5758-5767.
7. Berry, K. J .; Clark, P. E.; Gunter, M. J .; Murray, K. S.
Nouv. J. Chim. 1980, 4, 581-585.
1 8 . Gunter, M. J .; Mander, L. N. J. Org. Chem. 1981, 46, 4792-4795.
9. Lecas, A.; Levisalles, J .; Renko, Z.; Rose, E. Tetd. Letts. 1984,
25, 1563-1566.
10. Young, R.; Chang, C. K. J. Am. Chem. Soc. 1985, 107, 898-909.
11. Momenteau, M.; Mispelter, J .; Loock, B.; Bisagni, E. J. Chem. Soc.
Perkin Trans. 1983, 189-196.
12. Collman, J. P.; Reed, C. A. J. Am. Chem. Soc. 1973, 95, 2048-2049.
13. S o rrell, T. N. Inorg. Synth. 1980, 20, 161-169.
14. Collman, J. P.; Gagne, R. R.; Reed, C. A.; Halbert, T. R.;
Lang, G.; Robinson, W . T. J. Am. Chem. Soc. 1975, 97, 1427-1439.
15. Gottwald, L. K.; Ullman, E. F. Tetd. Letts. 1969, 36, 3071-3074.
16. E llio t t , C. M. Anal. Chem. 1980, 52, 6 6 6 - 6 6 8 .
17. Lindsey, J. J. Org. Chem. 1980, 45, 5215.
18. Collman, J. P.; Brauman, J. I . ; Collins, T. J .; Iverson, B. L.;
Lang, G.; Pettman, R. B.; Sessler, J. L.; Walters, M. A.
J. Am. Chem. Soc. 1983, 105, 3038-3052.
19. Sekine, M.; Hata, T. J. Org. Chem. 1983, 48, 3011-3014.
20. Sekine, M.; Masuda, N.; Mata, T. Tetrahedron 1985, 41, 5445-5453.
53
21. Beaven, G. R.; Holiday, E. R.; Johnson, E. A.; E llis , B.;
Mamalis, P.; Petrow, V.; Sturgeon, B. J. Pharm. Pharmacol. 1949,
i , 957-970.
22. Smith, K. M. In Porphyrins and Netalloporphyrins; Smith, K. M.,
Ed.; Elsevier S c ie n tific : New York, 1975; Chapter 1.
23. Momenteau, M.; Mispelter, J .; Loock, B.; Lhoste, J. M.
J. Chem. Soc. Perkin Trans. 1985, 61-70.
24. Storm, C. B.; Teklu, Y. J. Am. Chem. Soc. 1972, 94, 1745-1747.
25. Storm, C. B.; Teklu, Y.; Sokoloski, E. A. N. Y. Acad. Sci. 1973,
206, 631-640.
26. Mispelter, J .; Momenteau, M.; Lavalette, D.; Lhoste, J. M.
J. Am. Chem. Soc. 1983, 105, 5165-5166.
54
Chapter 3
Copper Complexes of Pincer Porphyrin
Once pincer porphyrin was synthesized and characterized, our
immediate goal was to metal late the porphyrin and grow single crystals
in order to determine the x-ray crystal structure. This was necessary
to ve rify our predictions concerning the precise structure of the
ligand. W e decided to begin with copper in the porphyrin ring because,
unlike ferrous porphyrin complexes, cupric porphyrin complexes are a ir
stable. They also c ry s ta llize re la tiv e ly easily.
Metal ation of the Porphyrin
Following the acetate method of porphyrin m etalation, 1 copper(II)
is easily inserted into the porphyrin ring using cupric acetate. X-ray
quality crystals were obtained by allowing pentane to diffuse into a
very concentrated chloroform solution. The x-ray crystal structure was
solved by Dr. W . R. Scheidt and co-workers. 2 The top view of this
structure is shown in Figure 3-1. The average Cu-N distance of 1.986A
compares favorably with the same distance (1.981A) in Cu(TPP) . 3
Another s im ila rity between these two copper structures is the slight
S ^ ru fflin g of the porphyrin core. This deviation from planarity
results in a contraction of the porphyrin core and, therefore, a
shorter M-N distance and may be due to packing effects in the crystal
la t t ic e . 4 The benzimidazole moieties lie approximately coplanar to the
porphyrin and are held in this orientation by hydrogen bonding between
the benzimidazole and the picket amides. This can be seen more clearly
in the closely related copper pincer porphyrin structure in which the
benzimidazole moieties are lacking the two methyl groups at the 5 and 6
position. 2 The reason for the alteration was to affect the s o lu b ility
and hopefully the c ry s ta l!iz a b ility of the metal complexes.
As seen from its top view (Figure 3-2) this related copper
complex, Cu(PincerP'), crystallized in nearly identical form (average
Cu-N = 1.968A). The side view (Figure 3-3) clearly indicates the
hydrogen bond between the benzimidazole lone pair and the adjacent
picket amide. The N-N distance is 3.00A, and s lig h tly longer in
Cu(PincerP), 3.05A. Both are somewhat longer than the typical distance
ascribed to secondary amide hydrogen bonding (2.8-2.9A). 5 The hydrogen
bonding and benzimidazole orientation are consistent with ring current
shifts in the N M R spectrum of the free porphyrin discussed in
Chapter 2.
Figure 3-1. The Cu(PincerP) molecule viewed from above the porphyrin plane. Reproduced from
reference 2 .
Figure 3-2. The Cu(PincerP/ ) molecule viewed from above the porphyrin plane.
Figure 3-3. Portion of Cu(PincerP') molecule shown to illu s tra te the hydrogen bonding between
the picket amide and the benzimidazole nitrogen lone pair. The N-N distance is 3.00A. Half of
the structure has been deleted for c la rity . Reproduced from reference 3.
! 59;
t |
! Coordination of Upstairs Copper
f
j The next step towards complete characterization was to introduce a|
1 second copper into the "upstairs" position, that is, between the two;
j J
| benzimidazoles. This reaction was necessary f ir s t ly to ensure that
j both benzimidazoles were capable of binding a single metal (although
I !
'molecular models showed no constraints), and secondly an x-ray crystal
i 1
(s tru c tu re would determine whether interactions between thel
I I
[benzimidazoles and the copper atoms were in tra -o r inter-m olecular. The'
i i
$ <
I desired product was the discrete 1:1 complex with intramolecular!
‘ interactions, since intermolecular bonding would lead to long chain;
I i
joligomers. \
' Attempts to coordinate C u (II) between the benzimidazoles were;
t !
(unsuccessful. Reaction of C u(II) salts such as CUSO4 and Cu(03 $CF3 ) 2 (
1
(with pincer porphyrin in order to form a binuclear cupric complex^
; resulted only in the mononuclear Cu(PincerP). Cu( I I ) complexes of
(benzimidazole have been synthesized both as polymeric benzimidazolate>
1
'complexes6' 8 and as tetrakis(benzimidazole) complexes such as;
1
I [Cu(benzimidazole)4 ]X2 , where X = C l, Br, I, NO3 , CIO4 , NCS, or
1 I / 2SO4 . 9 ’ 10 Perhaps the energy required to overcome the hydrogen bonds
jbetween the picket amides and the benzimidazoles in pincer porphyrin
| combined with the s ta b ility of the hexa-aquo cupric salts prevents the
1
■reaction from occurring.
Turning our attention instead to Cu( I ), we used several d ifferen t
cuprous salts including CutCh^CN^PFg, Cu(CH3 CN)4 BF4 , Cu(CH3 CN)4C1 0 4 ,
, and [Cu(0 3 SCF3 ) ] 2 *CgH6 , a ll of which have been previously
iprepared. 11-14 Copper(I) binds upstairs to the benzimidazoles
6 0
re la tiv e ly quickly (within minutes at room temperature in an inert
atmosphere dry box), and completeness of the reaction can be monitored
by t . l . c . In 1:1 THF/heptane Cu(PincerP) has an Rf=0.40 while the
product, [Cu(PincerP)Cu]X (X=PFg, CIO4 , BF4 , or O3 SCF3 ), remains at the
[
origin. There is usually a slight coloring at Rf 0.40 indicating the>
s ilic a gel plates may encourage demetal 1 ation. The v is ib le spectra,
show no change between starting material and product. Obviously the
addition of a second copper does not perturb the n electrons of the
copper porphyrin to any extent.
There is evidence of reaction in the vibrational spectrum of each
compound. The IR spectra of [Cu(PincerP)Cu]X are d iffe re n t from that
of Cu(PincerP) in two ways. F irs tly the d istin ctiv e bands of each
anion appear (PFg, 800 and 845cm- !; CIO4 , 1080 and 1100cm- !; BF4 , 1075
and 1090cm- !; O3 SCF3 , 625, 1025, and 1250cm- ! ) . Secondly the
disappearance of a sharp band at 1400cm"! occurs. (See Figures 3-4-
3 -7 .) W e speculate that this band is due to the hydrogen bonding
between the benzimidazole nitrogens and the amide groups of the
pickets, and that its disappearance is consistent with metal binding to
the two benzimidazoles, disrupting the hydrogen bond. The exact mode
of this band has not been determined. Supposing that i t was due to an
N-H bend of the picket amides (usually found from 1650 to 1450cm- ! ) 15
we wanted to exchange these protons with deuterium in the hopes that a
s h ift in this band could be detected and therefore positively assigned.
However, attempted deuteration of Cu(PincerP) with D2O under basic
(NaOH) or acidic (CD3COOD) conditions resulted in no change in the IR
spectrum. W e were able to drive this reaction using sodium metal, 18-
6.0 MICROMETERS 8 0 4.0 5.0 3.0
100
60 j
i
o'
Z
o
T h
< n
5
V)
z
<
G C
h -
40 [
600 WAVENUMUER lOM 1000 1800
Figure 3-4. Vibrational spectrum (KBr pellet) of Cu(PincerP)-3CHC13 . Note peak at 1400cm"* due
to hydrogen bond between benzimidazole nitrogen and picket amides.
0 1
2.5 3.0 4.0 5.0 6.0 MICROMETERS 0.0 10 ■ 16 ?i
T T T t r i
100
z
o
to
t o
s
t o
z
<
IT
> -
6 0 0 S C R WAVET1UM6ER (CM 1 6 0 0 MOO 2000 1 8 0 0 W AV ENU M H ER tC M J _
Figure 3-5. Vibrational spectrum (KBr pellet) of [CufPincerP)Cu]PFg. Bands due to anion appear
at 800 and 845cm"si. Note absence of band at 1400cm"1.
03
ro
TRANSMISSION (%
2.5 3.0 4.0 5.0- 6.0 MICROMETERS 8.0 10 16 2
60
40 ■ n :
? o
0
600 W A V E N U M O E R {C M »
V V A V T . N lJ f . m r R . C M i
Figure 3-6. Vibrational spectrum (KBr pellet) of [Cu(PincerP]Cu]C104 . Bands due to anion
appear at 1080 and 1100cm'1. Note absence of band at 1400cm"1.
6.0 MICROMETERS 8.0
M go____ \v a v e n ; j m s e h W AVENU M RER i CA 41.00
Figure 3-7. Vibrational spectrum (KBr pellet) of [Cu(PincerP)Cu]BF4 . Bands due to anion appear
at 1075 and 1090cm - 1. Note absence of band at 1400cm*
o r
4*
65
crown-6 , and D2O, but the appearance of multiple new bands indicated
that more than the picket amide protons were exchanged (Figure 3-8).
The substitution of deuterium in the amides produced bands in the 2200
to 2600cm"1 region which are attributed to an N-D stretching mode. 16
New bands in the 1400cm'1 region prevented the determination of whether
the original band had shifted. W e note that this 1400cm'1 band may
also be due to the C-N stretch of the amide (usually found from 1400 to
1250cm"1) 15 which could also be shifted by hydrogen bonding.
Even in the absence of a positive assignment for this band, its
disappearance in a ll of the bis copper complexes suggests that i t can
be used em pirically as an indicator of a second metal binding upstairs.
(This w ill become more important in the less well characterized Fe/Cu
complexes presented in Chapter 4.)
All four of the cuprous salts reacted with Cu(PincerP) to form the
desired 1:1 adduct, [Cu(PincerP)Cu]X, as shown by elemental analysis
and FAB-MS. Despite several attempts, x-ray quality crystals could not
be obtained. Regardless of using d ifferen t anions, a wide array of
solvent mixtures, and various techniques including lowered temperatures
and layering, [Cu(PincerP)Cu]X consistently crystallized as needles.
The reactions were carried out in THF/methanol mixtures and the
product invariably precipitated out. This low s o lu b ility is probably
the result of having charged species in low po larity solvents, but
could also arise from the formation of high molecular weight oligomers.
In the absence of an x-ray structure, we cannot d e fin itiv e ly d is tin
guish between these two p o s sib ilitie s , however the former explanation
is favored for two reasons. F irs tly , more polar solvents such as
TRANSMISSION <%)
6.0 MICROMETERS
6*
r 2 0 m r 4
EM E2
IVAVENUM8ER (CM WAVENUM8ER (CM )
Figure 3-8. Vibrational spectrum (KBr pellet) of deuterated Cu(PincerP)*3C 0Cl3 .
< r *
o >
67
dimethylformamide (DMF) were capable of dissolving the products and
secondly, we have determined the x-ray structure (Figure 3-4) of a
sim ilar binuclear complex, [(DMF)Zn(PincerP')Cu]PF6 . This contains the
altered benzimidazoles which have no methyl groups at the 5 and 6
positions. Crystals were grown by a member of our group, Dr. Steven J.
Rodgers, and the structure was solved by Dr. W . R. Scheidt and co
workers. 2 In this model zinc is the downstairs metal while Cu( I ) is
bound between the benzimidazoles. DM F provides a f if t h ligand to zinc
which lie s out of the porphyrin plane by 0.28A. The average Zn-N bond
length of 2.061A is sim ilar to that found in Zn(TPP)(H2 O). 17 The
structure of the binuclear complex is d is tin c tly d iffe re n t from that of
the mononuclear Cu(PincerP) in that the benzimidazoles no longer lie
approximately parallel to the porphyrin ring. Instead they become more
upright, scissoring away from the porphyrin resulting in a distance of
5.77A between the Cu atom and the mean porphyrin plane. The copper is
two coordinate as expected with an average Cu-N bond length of 1.864A.
This distance is consistent with a previous1 8 >19 bis-benzimidazole
copper complex [Cu2 (EDTB)] (ClO 4 )2 (average Cu-N = 1.873A).
68
G C
Figure 3-9. Side view of the [(DMF)Zn(PincerP')Cu]PFg molecule. The
Zn lie s 0.28A out of the plane of the porphyrin and tne Cu bound
between the two benzimidazoles lie s 6.04A above. Reproduced from
reference 2 .
Experimental
All cuprous reactions were conducted in a helium f il le d inert
, atmosphere glove box from Vacuum Atmospheres. The oxygen level was,
I maintained at less than lppm re la tiv e to a 5% hydrogen in nitrogen
'forming gas. Tetrahydrofuran (abbreviated THF) and benzene were
i
d is tille d from sodium/benzophenone inside the glove box. Methanol was
d is tille d from CaH2 under nitrogen. Column chromatography was
performed with pic grade s ilic a gel 60PF254 (Merck 7747). Thin layer
chromatography was performed on Anal tech S ilic a Gel GF plates.
Absorption spectra were obtained on a Shimadzu UV260 and vibrational
spectra were obtained on a Perkin Elmer Infrared Spectrophotometer 281.
Elemental analyses were performed at the University of C alifornia,
Berkeley, Microanaalytical Laboratory and FAB mass spectra were
performed at the Mass Spectrometry F a c ility , University of C alifornia,
San Francisco.
Cu(PincerP).CHClg
Pincer porphyrin (0.174g, 0.138mmol) was dissolved in chloroform
(25mL) and mixed with a solution of Cu(0Ac)2 'H20 (0.061g, 0.306mmol) in
methanol (15mL). The mixture was stirred for 15min. (The reaction
proceeded quickly but completeness could not be checked by t . l . c . since
the free porphyrin and the Cu complex move at the same rate in a ll
solvents systems used.) The solvents were removed and the residue was
redissolved in dichloromethane. F iltra tio n through a fin e f r i t removed
the excess copper(II) acetate. Pic grade s ilic a gel was added to the
solution, the solvent was removed, and the product was loaded onto a
70
2 X 4.5cm column packed with heptane. Elution with 4% methanol/
chloroform gave one major band which was collected and vapor diffused
with pentane to give purple-red crystals of the trichloroform solvate
( 0 .158g, 69%). Anal. Calcd. for Cygh^N^O^u-SCHC^: C, 58.49;
H, 4.55; N, 10.11; Cl, 19.18; Cu, 3.82. Found: C, 58.74; H, 4.50;
N, 10.20; Cl, 18.49; Cu, 3.95. FAB-MS: (M+H)+ 1304.
rCufPincerPlCulX. X=PF6. BF/|. CIO4 , or O3SCF3
In a typical reaction Cu(PincerP)-3 CHC13 (0.06g, 0.036mmol) was
dissolved in THF (20mL) and filte re d through a fine f r i t . One
equivalent of the appropriate copper salt was dissolved in methanol
(lOmL) and also filte re d through a fine f r i t into the solution of
Cu(PincerP). (In the case of [Cu(O3 SCF3 ) 2 ] 'CgHg, the solvents used
were either THF/methanol or neat benzene. The procedure was the same.)
Within 30min a red-orange precipitate f e ll out of solution which was
then filte re d and dried. The yield of [Cu(PincerP)Cu]X was essentially
quantitative in a ll cases. Elemental analysis and FAB-MS (correspon
ding to [Cu(PincerP)Cu]+) for the four copper complexes are as follows:
fCufPincerPlCulPFg Anal. Calcd. for C78H72N12O4CU2 PF6 : C, 61.89; H,
4.80; N, 11.11; Cu, 8.40. Found (average of four samples): C, 62.03; H,
4.87; N, 11.06; Cu, 8.33. FAB-MS: (M+H)+ 1368.
rCu(PincerP)CulBF/| Anal. Calcd. for C78 H72N12O4 CU2BF4 : C, 64.36; H,
5.00; N, 11.55; Cu, 8.73. Found: C, 64.08; H, 5.10; N, 11.76; Cu,
8.51. FAB-MS: (M+H)+ 1368.
71
rCu(PincerP)CulC10^ Anal. Calcd. for CygH^N^OgCi^Cl: C, 63.81; H,
4.95; N, 11.45; Cu, 8 . 6 6 . Found: C, 63.57; H, 4.89; N, 11.37; Cu,
8.93. FAB-MS: Highest peak at 1304 corresponds to loss of anion and 1
copper atom.
rCu(PincerP)Cul0 3 SCF3 Anal. Calcd. for C7gH72Ni207Cii2SF3 : C, 62.51; H,
4.79; N, 11.08; Cu, 8.37. Found: C, 62.88; H, 4.77; N, 10.42; Cu,
10.00. FAB-MS: (M+H)+ 1368.
Summary
Pincer porphyrin has been metallated and crystallized in the form
of Cu(PincerP)-3 CHC1 3 . Its x-ray crystal structure has been presented
which supports the suggestion of hydrogen bonding between the
benzimidazole nitrogen lone pairs and the picket amides. The binuclear
compounds [Cu(PincerP)Cu]X where X is PFg, BF4 , CIO4 , or O3 SCF3 , have
also been synthesized and thoroughly characterized although an x-ray
crystal structure was unobtainable. The binuclear complex of a closely
related porphyrin [ (DMF)Zn(PincerP')Cu]PFg has been presented in the
form of an x-ray crystal structure. This complex proves the a b ility of
pincer porphyrin to form discrete 1:1 complexes.
72
References
1. Buchler, J. W . In Porphyrins Dolphin, D., Ed.; Academic: New York,
1978; Vol. 1, Chapter 10, pp 389-483.
2. Rodgers, S. 0 .; Koch, C. A.; Tate, J. R.; Reed, C. A.;
Eigenbrot, C. W.; Scheidt, W . R. Inorg. Chem. 1987, 26, 3647-
3649.
3. Fleischer, E. B.; M ille r, C. K.; Webb, L. E. J. Am. Chem. Soc.
1964, 86, 2342-2347.
4. Scheidt, W . R. TIcc. Chem Res. 1977, 10, 339-345.
5. Hamilton, W . C.; Ibers, J. A. Hydrogen Bonding in SoTids
W . A. Benjamin: New York, 1968, Chapter 1.
6 . Ghosh, S. P. J. Indian Chem. Soc. 1951, 27, 710-712.
7. Inoue, M.; Kishita, M.; Kubo, M. Inorg. Chem. 1965, 4, 626-629.
8 . Cordes, M. M .; Walter, J. L. Spectrochim. Acta 1968, 24, 1421-
1435.
9. Bose, K. S.; Sharma, B. C.; Patel, C. C. J. Inorg. Nucl. Chem.
1970, 32, 1742-1743.
10. Goodgame, M.; Haines, L. I. B. J. Chem. Soc. (A) 1966, 174-177.
11. Kubas, G. J. Inorg. Synth. 1979, 19, 90-92.
12. Patch, M. A. Ph.D. Thesis, University of Southern C alifornia,
August, 1988.
13. Csoregh, I . ; Kierkegaard, P.; Norrestam, R. Acta Cryst. 1975, B31,
314-317.
14. Salomon, R. G.; Kochi, J. K. J. Am. Chem. Soc. 1973,95, 1889-1897.
15. Gordon, A. J .; Ford, R. A. The Chemists Companion, John Wiley &
Sons: New York, 1972; Chapter 4.
16. Krim, S. In Vibrational Spectra and Structure; Durig, J. R., Ed.;
Elsevier: New York, 1987; Vol. 16, Chapter 1.
17. Glick, M. D.; Cohen, G. H.; Hoard, J. L. J. Am. Chem. Soc. 1967,
89, 1996-1998.
18. Birker, J. J. M. W . L.; Hendricks, H. M. J .; Reedijk,
J. Inorg. Chim. Acta 1981, 55, L I7-18.
73
19. Hendricks, H. M. J .; Birker, P. J. M. W . L.; van R ijn, J .;
Verschoor, G. C.; Reedijk, J. J. Am. Chem. Soc. 1982, 104, 3607-
3617.
74
Chapter 4
Iron Complexes of Pincer Porphyrin
Confident in the capability of pincer porphyrin to serve as a
binucleating ligand and to c ry s ta llize w ell, we now turned our
attention to the metal necessary to mimic the active site of cytochrome
c oxidase, that is , iron. Our ultimate goal of course was to form an
Fe( 111)/C u (II) complex as found in the resting state of cytochrome c
oxidase, but due to the varying oxidation states of both metals, there
are d ifferen t routes which can be followed, and consequently models for
the other states of the enzyme can be produced. For example, F e (II)
was used to metal late the porphyrin and once Fe(PincerP) was
characterized, i t could be reacted either d ire c tly with copper salts or
i t could f ir s t be oxidized to F e (III) followed by addition of a copper
s a lt. This chapter describes the synthesis and characterization of the
ferrous and fe rric porphyrins as well as th e ir reactions with various
copper salts.
Synthesis and Characterization of Fe(PincerP)(THF)2
Pincer porphyrin was easily metallated using ferrous bromide and
weak base. This procedure, which avoids heating, has been used to
prevent atro p iso m e rizatio n o f a ,a ,a ,a -s u b s titu te d tetraphenyl
porphyrins. 1 A short alumina column was used to separate any excess
iron salt and the Fe(PincerP) was crystallized from THF/pentane forming
fra g ile purple crystals of the bis-THF complex. These crystals were
not of high enough quality to perform an x-ray structure analysis,
however an iron complex of the complementary ligand did c ry s ta lliz e as
the 5-coordinate Fe(PincerP')(l-t-Bulm ) where l-t-Bulm refers to 1 -t-
butylimidazole. This complex was crystallized by Dr. John R. Tate and
the crystal structure solved by Dr. W . R. Scheidt and co-workers. 2 Its
structure is shown in Figure 4-1 and i t is sim ilar to the copper
structures discussed in Chapter 3 in that there exists intramolecular
hydrogen bonds between the benzimidazole nitrogen and the picket
amides. The average N-N distance is s lig h tly longer in this case
(3.14A).
Characterization of Fe(PincerP)(THF)2 includes elemental analysis
and FAB mass spectrometry. The v is ib le spectrum in THF (Figure 4-2)
exhibits a Soret band at 432nm and a second band at 542nm which is
typical of 5-coordinate ferrous porphyrins. This compares favorably
with the v is ib le spectrum in THF, 429 (Soret), 545, and 590nm, of
Fe(TpivPP)(THF) 2 which is presumed 5-coordinate with the second THF
present in the la t t ic e . 1 The vis ib le spectrum of Fe(PincerP) in
benzene shows a double Soret at 420 and 447nm and another band at 542nm
Figure 4-1. A view of the Fe(PincerP') (l-t-B ulm ) molecule where 1 -t-
Bulm * 1-t-butylim idazole. Reproduced from reference 2.
77
i
J*
o o o o
Figure 4-2. V isible spectrum of Fe(PincerP) in THF (top) and benzene
(bottom). The double Soret confirms the absence of axial ligands in
the la tte r solvent.
0.25 0 .1 * } • > 0.25 0.125 0
« 1 r? 0 0 .0 — " ■ ■ ■ ■ ■ ■ » " I" " ■ ■ ■ I 7 0 0 .0
78
which indicates that the iron is 4-coordinate in this solvent (Figure
4 -2 ). This observation is important in confirming that the
benzimidazoles do not interact with the iron porphyrin eith er in te r- or
intra-m olecularly. This was a specific goal in the design of pincer
porphyrin as mentioned in Chapter 2.
There is nothing remarkable in the vibrational spectrum (Figure 4-
3) except the presence of the 1400cm"^ band found in a ll mononuclear
complexes of pincer porphyrin as explained in Chapter 3. The room
temperature magnetic moment is 5.23(Iq (measured by a SQUID magnetic
susceptometer) which confirms that i t is high spin F e ( II) , but the 77K
Mossbauer parameters are somewhat unusual. The isomer s h ift of
0.69mm/s is quite low for high spin Fe( I I ) (usually 0.9 to l.Omm/s),
and the quadrupole s p littin g of 2 . 00mm/s is also lower than typical
values (2.25 to 2.70mm/s).3
Enriching iron porphyrins with the 57Fe isotope serves to decrease
the amount of sample necessary for Mossbauer analysis. For example,
unenriched samples contain approximately 2% of the 57Fe isotope in its
natural abundance. For these samples, lOOmgs is needed to perform
re lia b le Mossbauer analysis, whereas only 5mgs is needed for a sample
which is 50% enriched. Purchasing the isotope in its reduced m etallic
form can be quite expensive ($25/mg) while the oxidized form of
is much easier to obtain. Previously the iron oxide has been treated
with concentrated hydrochloric acid to form the ir o n ( III) chloride,
which can either be used d irec tly to metal late porphyrins or can f ir s t
be electrochemically reduced to ^7 FeCl2 . 4 W e modified this procedure
to form 57 FeBr2 using HBr and m etallic iron as the reducing agent. W e
T R A N S M IS S IO N (-
6.0 MICROMETERS 8.0
•■ .m r, WAVF.NUMPER (CM J _ _ _ 2500 2 0 1 1 0 'SCO 1000 1-100 WAVE NUMBER (CM 'i 800 600
Figure 4-3. Vibrational spectrum (KBr pellet) of Fe(PincerP(THF)2 . Note peak at 1400cm"l which
is found in all mononuclear complexes of pincer porphyrin. ^
10
80
were then able to follow our normal procedure for metal 1 ating pincer
porphyrin, and the quantity of sample needed fo r Mossbauer analysis was
decreased several fold.
Mossbauer analysis of iron porphyrins is a powerful tool in
determining oxidation state and spin state of the metal center. In
order to compare the parameters found in pincer porphyrin complexes to
known ferrous and fe rric porphyrins, a plot of isomer s h ift vs.
quadrupole s p littin g was employed (Figure 4 -4 ). The data, mostly taken
from reference 3, include high spin and low spin ferrous porphyrins and
high, low, and intermediate spin fe rric porphyrins, and is tabulated in
Table 4-1. The diagram shows the d iffic u lty in distinguishing between
F e (II) low spin and F e (III) high spin complexes which was not
emphasized in a previous Mossbauer truth diagram. 5
Carbon Monoxide A ffin ity
While studying the properties of Fe(PincerP), we noticed that a ir
oxidation occurred at a much slower rate than other ferrous porphyrins.
Since oxidation was irreversible we were unable to measure the oxygen
a ffin ity d ire c tly , so we looked at the binding of another small
molecule, carbon monoxide, as a comparison. In this case, the C O
adduct could not be reversed by the usual technique of flushing with
nitrogen. Instead, the solution had to be evaporated to dryness under
vacuum and then fresh solvent introduced in order to ve rify the vis ib le
spectrum of the starting m aterial. To measure the C O a f fin ity , the
method followed was a modified version of Collman's8 which u tiliz e s
0.9-
0 . 8 -
0 .7-
0 . 6 -
0 .5- • &
0 .4-
0.3-
0.0
0.5 2.0 0.0 1.0 1.5 2.5 3.0 3.5 4.0
AEq , m m / s
Figure 4-4. Truth diagram for Mossbauer parameters of iron porphyrins. Symbols designate: low
spin ferrous, open triangles; high spin ferrous, open circles; low spin fe rric , fille d triangles;
high spin fe rric , fille d circles; and intermediate spin fe rric, squares. Compounds are listed in
Table 4-1. Data taken from reference 3.
82
Table 4-1. Mossbauer parameters for iron porphyrins. 3
low spin ferrous*3 6 AEq
Fe(PP)( Py)2 ° - 45 1.21
Fe(MP)(Py) 2 0.24 0.63
Fe(DPD) (Py) 2 ° - 27 1A1
Fe(TPP)(Py)? 0.40 1.15
Fe(PP)(Pi p) 2 0.49 1.42
Fe(TPP)(Pip)? 0.50 1.44
Fe(PP)(Im) 2 0.42 0.95
Fe(TPP)( Im) 2 0.45 1.06
high spin ferrous^
Fe(TPP)(THF) 2 0.95 2.66
Fe(TpivPP)(THF) 2 0.93 2.64
Fe(TPP)(2-MeIm)(EtOH) 0.92 2.26
Fe(TpivPP)(l-Melm)(EtOH) 0.88 2.32
low spin fe r r ic *3
Fe(PP)(Im)2Cl 0.24 2.30
Fe(PP)(Py)2Cl 0.23 1.88
Fe(PP)(4-Pi c )2C 1 0.10 1.97
Fe(PP)(4-NH2 Py)2Cl 0.10 1.93
Fe(PPD)(Im)2Cl 0.24 2.35
Fe(TPP)(Py)2Cl 0.16 1.25
Fe(TPP)(Im)2Cl 0.23 2.23
intermediate spin fe rr ic c
Fe(OEP)(BF4) 0.38 3.43
Fe(OEP)(C104) 0.37 3.57
[Fe(OEP)( EtOH) 2 ] Cl04 0.38 3.47
Fe(TPP)(C104)d 0.38 3.50
[Fe(OEP)(3-C1-Py)]C104e 0.36 3.23
high spin fe rr ic c
Fe(PP)Cl 0.35 0.83
Fe(MP)Cl 0.32 0.93
Fe(DPD)Cl 0.32 0.89
Fe(DP)Cl 0.24 0.91
Fe(0EP)Cl 0.41 0.93
Fe(TPP)Cl 0.41 0.46
Fe( PCIPP)CL 0.44 0.73
Fe( PFPP)Cl 0.38 0.85
Fe(PMXPP)Cl 0.37 1.03
83
(Table 4-1. continued)
Fe(DP)F 0.35 0.78
Fe(DP)N3 0.39 0.83
Fe(DPD)Br 0.38 1.02
Fe(TPP)Br 0.45 0.72
Fe(TPP)I 0.45 0.75
Fe(TPP)NCS 0.39 0.49
Fe(PClPP)I 0.50 1.04
Fe(PFPP)Br 0.43 1.04
Fe(PMXPP)Br 0.38 1.07
Fe(PMXPP)I 0.49 1.33
Fe(TPP)0Me 0.42 0.62
Fe(OEP)OMe 0.40 0.65
aData taken from reference 3 and references therein. S and AEq in mm/s
and 5 is re lativ e to m etallic iron. Abbreviations used: PP, proto
porphyrin; Py, pyridine; MP, mesoporphyrin dimethyl ester; DPD, 2,4-
diacetyldeuteroporphyrin dimethyl ester; TPP, tetraphenylporphyrin;
Pip, piperidine; Im, imidazole; THF, tetrahydrofuran; Melm, methyl-
imidazole; EtOH, ethanol; TpivPP, tetra(o-pivalamidephenyl)porphyrin;
Pic, picoline; NH?Py, aminopyridine; PPD, protoporphyrin dimethyl
ester; OEP, octaetnylporphyrin; DP, deuteroporphyrin dimethyl ester;
PC1PP, te tra (p -c h lo ro p h e n y l)p o rp h y rin ; PFPP, tetra(pentafl uoro-
phenyl)porphyrin; and PMXPP, tetra(p-methoxyphenyl) porphyrin.
bData obtained at 77K.
^Data obtained at 4.2K.
^From reference 5.
eFrom reference 6 .
changes in the vis ib le spectrum to calculate the equilibrium a ffin ity !
I or the P1/ 2C O (the partial pressure of carbon monoxide at which one1
| half the complex is C O bound). The a ffin ity is measured in th e [
!presence of 1,2-dimethyl imidazole to assure that a ll Fe(PincerP) is 5- 1
I
| coordinate rather than 6 -coordinate. Even in the highest
(concentrations of 1,2-dimethyl imidazole in toluene, Fe(PincerP) remains;
5-coordinate as shown by a Soret band at 443nm. (The ferrous porphyrin!
|w ill become 6 -coordinate in the presence of unhindered imidazoles such
as 1-methyl imidazole, with a Soret band at 430nm, indicating that axial
ligands of this size w ill f i t in the pocket created by the ligand
superstructure.)
*
The experiment consists of obtaining the v is ib le spectrum of;
Fe(PincerP) in a solution of 1,2-dimethylimidazole in toluene. Known
volumes of carbon monoxide are introduced into the cell using a gas
tig h t syringe and the spectrum measured again. The change in
absorbance at a specific wavelength is then measured and a plot of Pqq
vs. Pco/AA gives a straight lin e with the x-intercept equal to P1/ 2CO.
(For details of the theory and calculation see references 8 and 9 .)
)
The data and results of one such experiment is shown in Figures 4-5 and
!4 -6 . Analysis of this data led to a P1/ 2C O for Fe(PincerP) of 5 .3 to rr.
Previously reported P1/ 2C O values for iron ( I I ) porphyrins range from
2 . 5X10*4 to 1 .2 to rr. 10 These values include measurements for f la t
porphyrins such as tetraphenylporphyrin, picket fence porphyrins, and
strapped and capped porphyrins in which one face of the porphyrin is
^ t e r ic a lly hindered. The value of 5.3torr is s ig n ific a n tly higher than
any of these which indicates a lowered C O a ffin ity for Fe(PincerP).
I
\
I
T
Figure 4-5. Series of visible spectra of Fe(PincerP) in a toluene solution of 1,2-
dimethyl imidazole. Changes in the spectra occur as volumes of C O are added. The arrows indicate
the direction of the absorbance change as the C O adduct is formed. The nine spectra correspond
to 0.00, 0.25, 0.50, 0.75, 1.00, 1.50, 2.00, 3.00, and 5.00cc CO. The change in absorption at
442nm was used to calculate the P1/ 2CO.
P(CO)
Fe(PincerP) in 0.557m 1,2-di-
methylimidazole in toluene
Tonometer volume - 125.19cc
ccCO PfCQhtorr A.442nm
0.00 0 .00 2.126
0.25 1.581 1.725
0.50 4.736 1.326
0.75 9.449 1.033
1.00 15.694 0.847
1.50 24.983 0.727
2.00 37.214 0.635
3.00 55.255 0.568
5.00 84.573 0.517
slope = 1.7087
intercept = -5.33
P l/2C O = 5.33torr
O 10 20 30 40 50 60
P(CO)/dA
Figure 4-6. Data and graph used for the determination of P1/ 2C O for Fe(PincerP). CO
cn
This is surprising considering that 1-methylimidazole is capable ofj
binding inside the pocket of Fe(PincerP) and that the capped and^
strapped porphyrins appear to be at least, i f not more, s te ric a lly j
hindered than pincer porphyrin. j
1
In order to understand why this lowered C O a ffin ity occurred, we;
attempted to c ry s ta llize a C O adduct of Fe(PincerP). Toluene solutions!
1
Jof the iron porphyrin with 1 -methyl imidazole, or 1 , 2 -dimethyl imidazole, i
i
or 1-t-butylim idzaole were flushed with carbon monoxide and heptane!
I
allowed to diffuse into the solution. Only the 1,2-dimethyl imidazole!
i f
iCO adduct crys tallized , but due to the la b ilit y of the C O the crystals!
jhad to be manipulated under a C O atmosphere and a ll attempts to collect:
idata for an x-ray crystal analysis were unsuccessful.
j
j The vibrational spectrum (Figure 4-7) could be obtained only by
I preparing a Nujol mull in a C O f ille d glove bag and sealing the mull in ;
' I
, an a irtig h t c e ll. A moderately intense band at 1970cm"* corresponds
i
'to the Fe-CO stretch. A second interesting point is that the N-H amide^
; bands at 3380 and 3430cm- * in Fe(PincerP) as shown in Figure 4-3, now
reduce to a single band at 3380cm- *. Perhaps the binding of carbon
monoxide disrupts the hydrogen bond between the picket amides and the-
i
; benzimidazoles. This could explain the presence of one amide N-H band
f in the IR and the low a ffin ity of Fe(PincerP) for carbon monoxide. The
diagnostic peak at 1400cm- * that confirms this hydrogen bonding is
unfortunately obscured by a strong Nujol peak at 1375cm- *.
TRANSMISSION <%)
6.0 MICROMETERS 8 0
MOO WAVENUMBER (CM ;i 800
Figure 4-7. Vibrational spectrum (Nujol mull under CO) of Fe(PincerP)(l,2 -Me2 lm)(C0 ). Peak at
1970cm'1 corresponds to carbonyl stretch. Note single amide peak at 3380cm"1 corresponding to
N-H stretch of amides.
| 89
I
i Ir o n ( III) Complexes
}
j The final product in the oxidation of open face ferrous porphyrins,
i
is invariably the fi-oxo bridged dimer. 11 This product is avoided in
i \
| proteins such as hemoglobin simply because the polypeptide chain,
jprovides ample steric hindrance to block the porphyrin face. Quite a!
few of the recently synthesized derivatized porphyrins also provide the
j steric hindrance needed to either disfavor the /j - o x o dimer in
preference for the hydroxo complex or to allow an equilibrium mixture
, of both products. Porphyrins bulky enough to s ta b ilize F e ( III) hydroxo
complexes include strapped porphyrins such as Gunter's pyridyl
■strapped porphyrin12 and Momenteau's basket handle porphyrin, 13 ortho
substituted tetraphenyl porphyrins such as te tra k is (2 , 6 -difluorophenyl)
p o rp hyrin, 14 te tra m e s ity l p o rp hyrin, 15 and tetranicotinam ide
porphyrin, 16' 17 as well as porphyrins containing anthracene rather than
phenyl rings at the meso positions of the porphyrin, 1 8 ’ 19 and other
porphyrins. 2 0 ’ 21
The F e ( III) hydroxide can be formed by oxidation of the F e (II)
porphyrin or by hydroxide metathesis of the F e ( III) chloride. In some
> cases this can result in the iron ( I I I ) hydroxide exclusively, but
usually an equilibrium mixture of both the hydroxide and the /i-oxo
dimer occurs. These can often be separated by chromatography and both
complexes have been isolated and fu lly characterized for many of the
porphyrins mentioned.
W e produced the hydroxide of Fe(PincerP) by forming the Fe( I I I )
chloride and then treating with sodium hydroxide. This resulted in a
mixture of the /i-oxo dimer and the Fe ( I I I ) hydroxide which were
O'OSl
90
4x
5*
Figure 4-8. Visible spectrum 1n THF of Fe(PincerP)Cl (top),
Fe(PincerP)OH (center), and [Fe(PincerP) ] 2 0 (bottom).
421 . • w o 041 ‘ O' £ * 0
separated by column chromotagraphy. Since Fe(PincerP)OH was easily:
converted to [Fe(PincerP)^O, special care had to be taken once i t was
(p u rifie d to avoid acid and increased temperatures or an equilibrium
♦
mixture would reform. |
The v is ib le spectra of the chloride, the hydroxide, and the /x-oxo
i i
; dimer in THF are sim ilar yet d is tin c t (Figure 4 -8 ). The Soret band f o r ’
i
■ Fe( PincerP)Cl appears at 424nm and there is also a unique band at 510nm!
: which is typical of fe rric porphyrin complexes. The jx-oxo dimer Soret!
(appears at 415nm with another band at 570nm and a shoulder at 611nmJ
i
1 Fe(PincerP)OH has a Soret at 420nm. This bathochromic s h ift has beenj
i :
(observed for several of the hydroxo complexes mentioned above. The
' I
|second band in this complex appears at 573nm. Due to the s im ila ritie s 1
j i
' in these v isib le spectra, i t is not possible to determine the purity of:
i ,
! ,
I the hydroxo complex by this method since small amounts of the /x-oxoi
jdimer could go undetected. T .l.c . appears to be the best indication
, i
: of pu rity, however this must be conducted in acid-free solvents and'
i
re la tiv e ly quickly since s ilic a gel encourages the conversion of the;
! hydroxo complex to the /x-oxo dimer.
i The IR of the fi-oxo dimer shows the expected Fe-O-Fe stretch at:
1865 cm'1, while the hydroxide lacks any significant bands between 1000
I t
and 800cm'1 (Figure 4-9 ). The usual O H band in the 3400 region could
i not be detected in Fe(PincerP)OH due to the presence of a broad water
band as well as the porphyrin amide bands in the same region. There is
; however, a unique, very intense band at 1385cm"1 which is only seen in
: the hydroxo complex. This band is most lik e ly caused by the O H bending
| ,
[mode which often appears between 1 4 0 0 and 1250cm'1. 22
92
fV.ICRl.V If'T i'V S
800
M IC R O M ^ f C H S
40
W A VEMUMftERfCM 1 800 1000 600
Figure 4-9. Vibrational spectrum (KBr p e lle t) of [FefPincerPJUO
(top), Fe-O-Fe stretch at 865cm"1, and Fe(PincerP)OH (bottom), O H bend
at 1400cm"1.
93
FAB mass spectrometry of [Fe(PincerP) ] 2 0 shows a parent peak at
2611 confirming i t is dimeric. Unfortunately, th is technique appears
to be too harsh on Fe(PincerP)OH since the highest peak at 1297
corresponds to Fe(PincerP) and hence loss of the axial ligand.
The effective magnetic moment of the hydroxide at 300K is 5.7^b
consistent with high spin fe rric , and the ESR spectrum of a frozen
toluene solution exhibits g values at 5.8 and 2.0 also typical of high
spin fe rric .
Reactions with Copper(I) Hexafluorophosphate
The f ir s t attempt to form an iron/copper complex was to add
Cu(CH3 CN)4 PFg d ire c tly to Fe(PincerP) as we did with Cu(PincerP). The
ferrous porphyrin was dissolved in THF while the copper salt was
dissolved in either THF or methanol and the two combined. I f one
equivalent of copper was used, the reaction was incomplete as shown by
UV-vis and t . l . c . I f excess copper was used the in it ia l product showed
a vis ib le spectrum characteristic of Fe( I I I ) , 419 (Soret), 545, 610,
and 644nm (Figure 4-10). Recall that the Soret bands fo r Fe(PincerP)Cl
and Fe(PincerP)OH appear at 424 and 420nm, respectively. The Mossbauer
spectrum of this product using an 57pe enriched sample is quite
unusual. At 77K a single broad signal appears at 5=0.10mm/s and
AEg=0.0mm/s, which does not help in identifying the oxidation state of
the iron.
C rystallization of this from 1:1 THF/methanol vapor diffused with
heptane produced bow shaped clusters of needles or fra g ile crystals.
Unfortunately, the crystals did not d iffra c t w ell. The vis ib le
94
7x
Figure 4-10 Visible spectrum in THF of reaction of Fe(PincerP)(THF)?
and Cu(MeCN)4 PFc before (top) and a fte r (bottom) c ry s ta lliz a tio n from
THF and methanol.
95
spectrum of this solid was s lig h tly altered from the original product
with bands at 420 and 570nm (Figure 4-10), and was essentially
identical to that of Fe(PincerP)0H. Elemental analysis of this solid
showed a 1:1 Fe/Cu ra tio indicating that Cu was s t i l l bound. One
possible formulation for this product is Fe(PincerP)OHCuPFg. The
original product must also contain copper and so could possibly be
Fe(PincerP)PFgCuPF5 . I t appears that the PFg anion slowly exchanges
due to water present in the solvents. The FAB-MS of this product shows
no presence of Cu or axial ligand, only Fe(PincerP), but we have seen
the loss of axial ligand in the case of Fe(PincerP)OH, and i t is
possible that the conditions of the experiment are too harsh to allow a
weakly bound bis-benzimidazole copper to survive. (In one of the
dinuclear copper complexes presented in Chapter 3, Cu(PincerP)CuC1 0 4 ,
FAB mass spectrometry also caused the loss of one copper.)
Reactions with Copper(I) T rifla te
The reaction products of Fe(PincerP)(THF)2 and [Cu(0 3 SCF3 ) ] 2 *C5 Hg
in benzene have not been fu lly characterized. T .l.c . in 1:1
THF/heptane shows a reaction has occurred with the product remaining at
the orig in. The v isib le spectrum also changes from the double Soret of
Fe(PincerP) in benzene at 420 and 447nm to a single Soret at 404nm as
well as another band at 524nm. The spectrum is sim ilar to that of
Fe(TPP)C1 0 4 , an admixed intermediate spin fe rric porphyrin, 6 405
(Soret) and 510nm in toluene, which supports a formulation of
Fe(PincerP)(O3 SCF3 ) but whether copper is bound upstairs is unknown.
The Mossbauer parameters for an ^ F e enriched sample indicate that
96
there are at least two products formed. Part of the mixture, 39%, has
an isomer s h ift of 0.43mm/s and a quadrupole s p littin g of 3.42mm/s,
while another component, 61%, has an isomer s h ift of 0.59mm/s and a
quadrupole s p littin g of 2.26mm/s. The f ir s t set of parameters f i t
quite well to an F e ( III) intermediate spin porphyrin complex, (compare
Fe(TPP)C104 with 5=0.38mm/s and AEq=3.48mm/s), 6 while the second set
are sim ilar to, but not exactly lik e , the parameters observed for the
starting material Fe(PincerP)(THF) 2 > 6=0.69mm/s and AEq=2.00mm/s. I t
is possible that changing the solvent to benzene and therefore
changing the environment around iron is responsible.
In order to avoid the oxidation of Fe(PincerP) upon addition of
cuprous salts, we attempted to sta b ilize the Fe( I I ) state by forming
the carbon monoxide adduct. Once the copper was chelated, the C O could
easily be removed under vacuum. Because of the use of CO, these
reactions had to be performed using Schlenk techniques rather than in
the glove box. A benzene solution of Fe(PincerP) was flushed with dry
carbon monoxide gas to form the C O adduct with vis ib le spectrum of 424
(Soret) and 540nm. A benzene solution of [Cu(0 3 SCF3 ) ] *CgHg was added
and immediately a red-orange precipitate formed. In one experiment,
this solid was filte re d and allowed to dry under C O and transferred to
a glove bag f ille d with CO. The vibrational spectrum of a Nujol mull
revealed two carbonyl stretches at 1980 and 2100cm "presum ably due to
Fe-CO and Cu-CO. The visib le spectrum of this C O complex in THF looks
exactly lik e Fe(PincerP)C0.
In another experiment, this solid was placed under vacuum which
caused a color change to purple-brown. Elemental analysis of this
6.0 M IC R O M ETER S 8.0 4.0 5 0 3.0 2.5
100
O 'J
z
0
tn
w
1
(0
z
<
c c
(-
600 V.'AVEN1 JMROI (CM , 1600
WAVENUMCSER iCM i 4000
Figure 4-11. Vibrational spectrum (KBr pellet) of product from reaction of Fe(PincerPlC0 and
copper(I) t r if la t e after being put under vacuum to remove CO. Note absence of 1400cm'l peak.
98
solid consistently resulted in a much higher percentage of copper than
anticipated. Its IR spectrum (Figure 4-11) contained no carbonyl peaks
in the 1900-2100cm'1 region as expected and the diagnostic 1400cm"1
peak was also absent indicating the copper was indeed bound to the
benzimidazoles. However, i f the solid was exposed to C O before the
Nujol mull was prepared, only one C O peak reappeared at 2100cm' 1
suggesting that eith er only one metal was present, or one metal was
unable to lig ate carbon monoxide a second time. The complexity of the
Mossbauer spectrum suggested the presence of at least two and possibly
more components.
I f this solid was brought inside the glove box and dissolved in
THF, i t produced a vis ib le spectrum with bands at 404 (Soret), and
422nm. This spectrum was essentially identical to that of the reaction
of Fe(PincerP) and copper(I) t r i f l a t e . Flushing this THF solution with
C O slowly reproduced a spectrum sim ilar to the original Fe(PincerP)C0
spectrum with bands at 421 (Soret) and 538nm. Vapor diffusing the THF
solution with heptane produced dark needles whose Mossbauer parameters
also revealed at least two components. 48% of the compound showed
parameters sim ilar to intermediate spin fe rric porphyrins, 5=0.37mm/s
and AEq=2.98mm/s and could be the fe rric porphyrin complex with a
t r i f l a t e anion. Whether copper is bound is unknown. The second
component, 52%, showed an isomer s h ift of 0.46mm/s and a quadrupole
s p littin g of 2.48mm/s. These parameters are atypical of any iron
porphyrin complex and this component has not been id e n tifie d . Several
attempts to c ry s ta lliz e and purify the product of th is reaction fa ile d
to produce less than two components in the Mossbauer spectrum.
99
Support for the formulation of a fe rric t r i f l a t e complex comes
from the reaction of the fe rric hydroxide with copper(I) t r i f l a t e .
Fe(PincerP)OH was dissolved in dry benzene showing a v is ib le spectrum
with bands at 423 (Soret), 509, and 573nm. [Cu(0 3 SCF3 ) ] 2 ’ C6 H6 was
added and a dark brown precipitate immediately formed. This was
filte re d leaving a perfectly clear solution. The visib le spectrum of
this solid in THF shows a Soret at 403nm and another band at 522nm,
identical to those from the two reactions of Fe(PincerP) and copper(I)
t r i f l a t e presented above. The IR spectrum of this solid shows no peak
at 1400cm'1 and bands due to the t r if la t e anion appear at 635, 1025,
1165, 1210, and 1240cm'1.
This set of reactions each resulted in a fe rric t r i f l a t e complex
and we were unable to determine whether Cu( I ) t r i f l a t e was bound
between the benzimidazoles. I t is possible that forming the carbon
monoxide adduct helped to s ta b ilize F e ( II) , but as soon as the C O was
evacuated and the product dissolved in THF, oxidation to the fe rric
complex occurred. I t is puzzling that even in the reactions in which a
precipitate formed, the Mossbauer spectra consistently showed the
presence of more than one complex (usually a 50:50 mixture) and pure
products were unobtainable.
Reactions with Copper(I) Chloride
I f Fe(PincerP) (THF)2 was mixed with CuCl in THF, no reaction
occurred, but i f Fe(PincerP)0H was used instead, a reaction did occur
as shown by t . l . c . The vis ib le spectrum, however, was identical to
starting m aterial. This does not necessarily indicate that copper has
100
not been chelated by the ligand since in the bis-copper complexes,
[Cu(PincerP)Cu]X, the second copper has no influence on the visib le
spectrum. The solution was filte re d and diffused with pentane to
produce a dark precipitate which analyzed for the 1:1 Fe/Cu complex,
Fe(PincerP)OHCuCl-2THF. The Mossbauer analysis with 6=0.43mm/s and
AEq=0.71mm/s is typical of high spin Fe( I I I ) .
Reactions with Copper(I) Cyanide
W hen the reaction between the Fe(PincerP) and CuCN is carried out
in a non-coordinating solvent, such as toluene, a 1:1 iron/copper
precipitate is formed as shown by elemental analysis. The Mossbauer
parameters for this complex, 6=0.89mm/s and AEq=1.97mm/s, are typical
of high spin F e (II) , and suggest that the cyanide ligand is not bound
to iron since fe rric cyanide porphyrins are invariably low spin. The
vibrational spectrum shows one cyanide stretch at 2119cm'1 presumably
due to a copper bound cyanide.
Dissolving this iron/copper complex in THF produces a visible
spectrum with bands at 420 (Soret) and 530nm. When heptane is allowed
to diffuse into this solution, dark purple crystals form which have
d iffe re n t properties from the original precipitate. The vibrational
spectrum now shows two cyanide peaks at 2120 and 2070cm"1 . This same
complex can also be produced by conducting the original reaction in THF
rather than toluene. The identical visib le spectrum is observed and
the IR shows cyanide peaks at 2130 and 2070cm"1 (Figure 4-12). The
Mossbauer spectrum for this complex consists of two quadrupole
doublets. The majority of the m aterial, 91%, has an isomer s h ift of
6.0 M IC R O M ETER S 8.0
I'iit 'iiiii: : .: : I l L d u i i i l i i l i b l i f l t i L ' f * ; ? t ; : iV m l V l i i l i i i H M i M
: i t i ! i ;
- f l)
M I S
.VAVENUMuCR tuM » 80'J
.VAVEMUMRER (CM
•ion
Figure 4-12. Vibrational spectrum (KBr pellet) of product from reaction of Fe(PincerP)(THF)? and
CuCN in THF. Two cyanide stretches appear at 2130 and 2070cm'1.
102
0.37mm/s and a quadrupole s p littin g of 1.17mm/s, while the remaining
9% has an isomer s h ift of 0.33mm/s and a quadrupole s p littin g of
1,92mm/s.
There have been several N M R studies of cyanide derivatives of iron
porphyrins, however, only a few have been characterized in the solid
s ta te. 2 3 * 24 In order to compare the physical parameters of our
products to those of known compounds, a series of iron cyanide
porphyrins were synthesized. First we reacted Fe(PincerP)(THF)2 with
tetraethyl ammonium cyanide to produce [Fe(PincerP)(CN)]Et4 N. Its
v is ib le spectrum in THF showed a Soret at 428nm and a second band at
530nm. Its Mossbauer parameters at 77K were 6=0.39mm/s and
AEq=1.31mm/s. The vibrational spectrum displayed one cyanide stretch
at 2070cm'1 obviously due to an iron bound cyanide (Figure 4-13).
Another ferrous porphyrin, [Fe(TpivPP)(CN)]Et4N, was also
synthesized and showed sim ilar visib le spectrum with bands at 427
(S o ret) and 529nm and Mossbauer parameters, 6=0.35mm/s and
AEq=1.85mm/s. I t also showed an identical cyanide stretch at 2070cm'1
in the vibrational spectrum.
One more compound, [Fe(TpivPP)(CN)2 ] K, an F e ( III) bis-cyanide was
synthesized. In this case, even though the vis ib le spectrum showed a
single Soret at 435nm, and the elemental analysis agreed with a bis-
cyanide formulation, the Mossbauer spectrum consistently showed more
than one component with 30% having 6=0.43mm/s and AEg=2.0mm/s, and 70%
having 5=0.20mm/s and AEQ=0mm/s. Also the absence of any cyanide peaks
in the vibrational spectrum was quite suspicious, although the
intensity of cyanide stretches is generally weak.
16 2 6.0 M IC R O M ETER S 8.0
'! : i
■ i o o o |CM . 2 ? 0 0 _ _ 2 0 0 0 1 8 0 0 1 6 0 0
ML") VVAVEiIUMBER (CM ■ / 800 600
appears^at^2070cm'^iOna1 SpeCtrum {KBr Pe lle t) of [Fe(PincerP)(CN)]Et4N. Single cyanide stretch
C O
104
Returning to the two products formed in the reaction of
Fe(PincerP)(THF)2 and CuCN in THF, there are several possible expla
nations. The cyanide band at 2070cm'1 in the vibrational spectrum is
obviously due to an iron bound cyanide. The same peak is found in
both [Fe(TpivPP)(CN)]Et4 N and [Fe(PincerP)(CN)]Et4 N and these compounds
are the f ir s t ferrous cyanide porphyrin complexes characterized.
The second cyanide peak at 2130cm"1 could be caused by a fe rric
mono-cyanide or bis-cyanide complex. For example, bis-cyano complexes
of ir o n ( III) protoporphyrinIX and tetraphenyl porphyrin exhibit
cyanide stretches at 2112 and 2120 cm'1, respectively, 2 4 »22 while
Fe(TPP)(CN)(py) 22 shows a band at 2130cm"1. The Mossbauer parameters
of the product (91%, 5=0.37mm/s and AEq=1.17mm/s and 9%, 5=0.33mm/s and
AEq=1.92mm/s) are consistent with F e (II) low spin and F e ( III) low spin,
respectively, lending support to a fe rric cyanide complex. The bis-
cyanide can be ruled out since analysis of the product from the
reaction in toluene shows a 1:1 Fe/CuCN complex, and this product
crystallized in THF gives two cyanide peaks and at the same time shows
no ferrous THF complex in the vis ib le spectrum.
This cyanide stretch at 2130cm'1 might also be caused by a copper
bound cyanide. Free CuCN exhibits a cyanide stretch at 2170cm"126
which tends to rule this out, but association with THF could cause a
s h ift in this peak. Cu(PincerP)CuCN shows a cyanide stretch at
2120cm"1. (This complex was not presented in Chapter 3 since elemental
analysis consistently showed a very high copper content.) The problem
with this explanation is that i f there is only one equivalent of
cyanide per iron and i t is bound to copper, rather than iron, the
105
Mossbauer should show the presence of a high spin ferrous porphyrin,
which is not the case.
The second cyanide stretch may also be explained by a bridging
cyanide between iron and copper, which would exhibit a peak at higher
frequency. 27 For example, Gunter's28 F e ( III) tetranicotinamide
porphyrin C u (II) cyanide complex, which is proposed to contain an
Fe-CN-Cu moiety, exhibits a cyanide stretch at 2150cm“l . S im ilarly, a
peak at 2162cm- ^ has been assigned to the bridging cyanide between iron
and copper in the polymeric material 3[Cu(dien)] *2[Fe(CN)6] *6 ^ 0 , where
dien is diethylenetriam ine. 29 The existence of one isomer which does
not contain a cyanide bridge may be due to the cyanide binding on the
open face of the heme rather than inside the ligand superstructure, ie.
on the side of the copper.
These are a few of the possible explanations for an equilibrium
mixture of products, although without structural characterization, i t
is uncertain whether copper is in fact bound between the benzimida-
zoles. However, in view of the previously characterized Cu(PincerP)CuX
complexes and the crystal structure of Zn(PincerP')CuPFg, i t is
certainly lik e ly .
Experimental
All reactions were conducted in a helium f il le d in ert atmosphere
glove box from Vacuum Atmospheres, unless noted otherwise. The oxygen
level was maintained at less than lppm re la tiv e to a 5% hydrogen in
nitrogen forming gas. Tetrahydrofuran (THF), benzene, toluene,
heptane, and pentane were d is tille d from sodium/benzophenone inside the
106
glove box. Methanol was d is tille d from CaH2 under nitrogen. All other
solvents were used without further p u rificatio n .
Column grade s ilic a gel was EM(Merck)100, 70-230 mesh and p .I.e .
grade s ilic a gel was 60PF254 (Merck7747). Thin layer chromatography
was performed on Analtech S ilic a Gel G F plates. Alumina was activated
at 430°C under high vacuum for several hours, sealed, cooled, and
brought into the glove box. I t was then deactivated with d is tille d
water, 10% w/w.
Absorption spectra were obtained on a Shimadzu UV260
spectrophotometer. Vibrational spectra were obtained on a Perkin Elmer
Infrared spectrophotometer 281. Elemental analyses were performed at
the University of C alifornia, Berkeley, Microanalytical Laboratory and
fast atom bombardment (FAB) mass spectra were performed at the Mass
Spectrometry F a c ility , University of C alifo rn ia , San Francisco.
Mossbauer spectra were performed by Dr. Ben Shaevitz in Prof. George
Lang's group at Penn State University.
FefPincerPl(THFlg
PincerP’F^O (0.10g, 0.079mmol) was dissolved in 1:1 THF/benzene
(60mL) and FeBr2 (0.10g, 0.46mmol) was added. The solution was stirred
overnight. Completeness of the reaction was checked by t . l . c . A small
aliquot was brought outside the glove box and allowed to oxidize. I t
was spotted on a t . l . c . plate next to starting material and exposed to
aqueous NH4O H to convert the ferrous porphyrin to the fe rric hydroxide.
Elution with 4:3:3 dichloromethane/hexanes/ether brought the free
porphyrin to Rf0.40 and the Fe( I I I ) hydroxide to RfO.10 and a spot
107
remaining at the origin. W hen the reaction was complete, K2CO3 (0.10g,
0.72mmol) was added and the solution stirred lh r. ( I f the base was
added at the beginning of the reaction, a fine precipitate invariably
formed which was only soluble in methanol.) The solution was then
filte re d and reduced under vacuum to h a lf the volume. Activated
neutral alumina was used to separate the excess ferrous bromide. A 2in
plug was rinsed with THF and the product filte re d through the alumina
rinsing with further THF to collect a ll of the purple red solution.
The solvent was evaporated to dryness and the residue redissolved in
THF, filte re d through a fine f r i t and vapor diffused with pentane.
A fter several days, large rectangular crystals formed (0.085g, 75%)
which were filte re d and rinsed with pentane. Anal. Calcd. for
c78H72N12°4Fe' 2THF: c > 71.64; H, 6.16; N, 11.66; Fe, 3.87. Found,
(average of 3 samples): C, 71.67; H, 6.12; N, 11.83; Fe, 3.57. FAB-MS:
(M+H)+ 1297. Xmax: (THF) 432 (Soret) and 542nm; (benzene) 420, 447,
and 542nm. Mossbauer: (77K, 0G) 6=0.69mm/s, AEg=2.00mm/s.
Meff=5 -23M B*
57fj|Br2
5 7 Fe203 (0.52g, 3.2mmol) was dissolved in HBr (40mL) by warming
the dark orange solution in a hot water bath for several hours. The
flask was flushed with nitrogen and m etallic iron powder (H2 reduced,
0.3g, 5.3mmol) was added. A fter the solution had turned pale green
( l / 2 hr) i t was filte re d and the solvent removed under vacuum.
C rystalline needles formed which were dried under vacuum then
transferred to the glove box. They were dissolved in methanol,
108
filte r e d , and the solvent removed under vacuum while heating the flask
(5hrs). This produced a yellow powder of approximately 50% enriched
57 FeBr2 (2.36g, 93%).
FefPincerPlOH and fFe(PincerP)IgO
PincerP was metallated following the same procedure as above, but
instead of working up the reaction, i t was brought outside the glove
box and evaporated to dryness. The residue was dissolved in 5%
methanol in chloroform and loaded onto a s ilic a gel column (2.5 X
30cm). Elution with 5% methanol in chloroform le f t an orange band of
oxidized iron bromide at the origin and allowed the major band of
metalloporphyrin to be collected. The resulting solution was washed
with conc. H C 1 (lOOmL), 10% aqueous NaCl (lOOmL), 10% aqueous NH4O H (2
X lOOmL), and again with 10% aqueous NaCl (2 X lOOmL). The solution
was dried with anhydrous NagSO^ filte re d and the solvent removed at
room temperature. (Increased temperatures used to remove solvent
resulted in a greater ra tio of /j- o xo to hydroxo.) Column chroma
tography was used to separate the /x-oxo and hydroxo components. In
order to avoid conversion to the Fe( I I I ) chloride, a ll residual H C 1 in
chloroform had to be neutralized by f iltr a tio n through basic alumina.
Then a chloroform slurry of p .I.e . grade s ilic a gel was exposed to
conc. NH4O H in a covered beaker for lh r. This was used to load the 2 X
10cm column and the hydroxo, n~oxo mixture was loaded as a chloroform
solution. Elution with 30:5:1 neutral chloroform/ether/ methanol
resulted in two major bands. The f ir s t fraction was [Fe(PincerP)]20.
The solvent was removed with a small addition of heptane at the end
109
resulting in a purple-black crystallin e product, Rf0.34 (30:5:1
chloroform/ether/methanol). Amax (THF): 415 (Soret), 570, and 611nm.
FAB-MS: (M+H)+ 2611. IR: (KBr p e lle t) uFe-O-Fe 865cm-1.
The second fraction was Fe(PincerP)OH. A fter addition of heptane
the solvent was removed (without increased temperatures) resulting in a
brown-green crystallin e product, Rf0.20 (30:5:1 chloroform/ether/
methanol). Anal Calcd. for C7gH73Ni205 Fe-CH30 H: C, 69.69; H, 5.93; N,
12.20; Fe, 4.05. Found: C, 69.89; H, 5.94; N, 11.74; Fe, 3.34. Amax:
(THF) 420 (Soret) and 573nm. /ieff=5.7/zg
Reaction of Fef PincerP) (THFlg and Cu(MeCN)/|PFg
Fe(PincerP)(THF)2 (0.03g, 0.021mmol) was dissolved in THF (30mL)
and filte re d through a fine f r i t . Cu(MeCN)4 PFg (0.02g, 0.054mmol) was
dissolved in methanol (15mL) and also filte re d . The two solutions were
combined and stirred lh r. T .l.c . in 1:1 THF/heptane was used to
determine whether the reaction was complete. Any unreacted Fe(PincerP)
moved to Rf0.40 while the product remained at the orig in. The visible
spectrum in THF also showed a reaction had occurred, 419 (Soret), 545,
610, and 644nm. The solvent was reduced to lOmL, filte r e d , and
diffused with heptane. Needles of lemon-shaped purple crystals formed
but the v is ib le spectrum of this product differed from the reaction
m ix tu re , 420 (S o r e t) and 570nm. A n a l. C a lc d . fo r
C8 H72Ni205 CuFePF6 *C7H16; C, 62.89; H, 5.54; N, 10.36; Cu, 3.92; Fe,
3.44. Found: C, 64.02; H, 5.63; N, 10.36; Cu, 4.01; Fe, 3.30.
Fe(PincerP)(THF)g and rCu(0 ?SCF3 ) l 2 .C6Hg '
Fe(PincerP)(THFJg ( 10mg, 0.007mmol) was dissolved in benzene
(lOmL) and filte r e d . [Cu(0 3 SCF3 )Ig'CgHg (25mg, O.5mmol) was dissolvedj
in benzene (lOmL), filte r e d , and combined with the Fe(PincerP)i
solution. The mixture was stirred 2hrs and the reaction was checked
i
for completeness by t . l . c . in 1:1 THF/heptane (the product remained at
the origin) and by vis ib le spectroscopy, Amax (benzene) 404 (Soret) and
524nm. The solvent was evaporated until a red-orange precipitate
formed. Mossbauer: (77K, 06) 61%, 6=0.59mm/s and AEq= 2. 26mm/s; 39%,
5=0.43mm/s and AEq=3. 42mm/s.
FefPincerPlCO and rCu(03 SCF3 n 2 .C6Hs
In an in ert atmosphere glove box, Fe(PincerP)(THF)g (30mg,
0.02mmol) was dissolved in benzene (15mL) and filte r e d into a schlenk
flask. [Cu(0 3 SCF3 ) ] 2 -CgH5 (54mg, O.llmmol) was dissolved in benzene
(lOmL) and filte re d into a schlenk flask. Both solutions were sealed,
brought outside the glove box, and flushed with a stream of dry carbon
monoxide for lh r. The copper salt solution was transferred into the
porphyrin solution and immediately a red-orange precipitate formed.
This was filte re d and treated in one of two ways. 1) I f allowed to dry
under an atmosphere of CO, and prepared as a Nujol mull in a C O f ille d
glove bag, the vibrational spectrum showed M-CO peaks at 1980 and
2100cnrl. Amax: (THF under CO) 422 (Soret) and 540nm. 2) I f dried
under vacuum for 15min, the solid changed to purple-brown. Amax: (THF)
404 (Soret) and 422nm; (THF under CO) 421 (Soret) and 538nm.
Mossbauer: complex spectra with at least two components. The solid was
i 111
i r
I crystal 1ized from THF/heptane to produce dark purple needles,
i Mossbauer: (77K, OG) 48%, 6=0.37mm/s and AEq=2.98mm/s; 52%, 6=0.46mm/s
i
and AEq=2.48mm/s. IR: (KBr p e lle t) t r i f l a t e bands at 630, 1020, 1200,
; and 1310cm“l.
FefPincerPlOH and rCuf0 3 SCF3 l l 2 .C6H6
I
Fe(PincerP)0H (20mg, 0.015mmol) was dissolved in benzene (15mL)
and filte r e d . [Cu^SCFsJ^'CgHg (45mg, 0.09mmol) was added and
immediately a dark brown precipitate formed. This was filte re d and
dried. \n ax: (^HF) 403 (Soret) and 522nm. IR: (KBr p e lle t) t r i f l a t e
bands at 635, 1025, 1165, 1210, and 1240cm-l.
FefPincerPlOH and CuCI
Fe(PincerP)0H (76mg, 0.058mmol) was dissolved in THF (15mL) and
CuCI (5.3mg, 0.054mmol) was added. The suspension was stirred
overnight. T .l.c . in 1:1 THF/heptane showed a reaction had occurred
with the product remaining at the origin, but the v is ib le spectrum was
identical to starting m aterial. The solution was filte re d and diffused
with pentane. A dark precipitate formed which was filte r e d and rinsed
with pentane (47mg, 60%). Anal. Calcd. for C78H73Nj205CuFe'2THF: C,
66.99; H, 5.83; N, 10.90; Cu, 4.12; Fe, 3.62. Found: C, 67.03; H, 5.13;
N, 11.03; Cu, 3.89; Fe, 3.40. Mossbauer: (77K. 0G) S=0.43mm/s and
AEq=0.71mm/s.
! FefPincerPI(THFIg and CuCN
! Reaction in toluene
i
t '
Fe(PincerP)(THF)2 (36mg, 0.025mmol) was dissolved in toluene
■ (40mL) and CuCN (20mg, 0.023mmol) was added. The suspension was
I
; stirred overnight to form a red-orange precipitate. This was filte r e d ,
rinsed and dried to give a purple solid (34mg, 90%). Anal. Calcd. for
c79H72N13°4CuFe,1-5C7H8 : c » 70.46; H, 5.56; N, 11.94; Cu, 4.17; Fe,
3.66. Found: C, 70.32; H, 5.59; N, 11.45; Cu, 4.50; Fe, 3.40. IR:
(KBr p e lle t) uCN at 2119cm"1. Mossbauer: (77K, 0G) 6=0.89mm/s and
AEq=1.97mm/s.
The product was dissolved in THF to give a v is ib le spectrum with
bands at 420 (Soret) and 530nm. The solution was vapor diffused with
heptane to give dark purple crystals. IR: (KBr p e lle t) uCN at 2120 and
2070cm-1.
Reaction in THF
Fe(PincerP)(THF)2 (36mg, 0.025mmol) was dissolved in THF (15mL)
and CuCN (2.5mg, 0.028mmol) was added. The suspension was stirred
overnight becoming a red-orange solution. Amax: (THF) 420 (Soret) and
530nm. The solution was filte re d and vapor diffused with heptane to
form dark purple crystals. IR: (KBr p e lle t) uCN at 2130 and 2070cm"1.
Mossbauer: (77K, 0G) 91%, 6=0.37mm/s and AEg=l. 17mm/s; 9%, 6=0.33mm/s
and AEq=1.92mm/s.
rFefTpivPPl (CN1 lEt/|N
Fe(TpivPP)(THF)2 (31mg, 0.026mmol) and Et4NCN (4mg, 0.026mmol)
were dissolved in warm THF. The solution was stirred overnight and
I 113
t ;
I
j then filte re d and vapor diffused with heptane. Clusters and square
i ‘
f la t crystals formed which were filte r e d , rinsed with heptane and
i '
tallowed to dry leaving the mono-cyano mono-THF adduct (29mg, 86% ).;
j ’
i Anal. Calcd. for C jyl^N jot^Fe: C, 71.49; H, 7.18; N, 10.83; Fe, 4.32.:
1 1
jFound: C, 71.28; H, 7.10; N, 11.01; Fe, 4.51. Amax: (THF) 427 (Soret)
and 529nm. Mossbauer: (77K, OG) 5=0.35mm/s and AEg=1.85mm/s. IR: (KBr
p e lle t) uCN at 2070cm"
i
rFe(TpivPP)(CN)2IK
Fe(TpivPP)Cl (0.77g, 0.70mmol) and KCN (0.20g, 3.07mmol) were
dissolved in THF (50mL) and methanol (5mL). The solution was stirred
until the v is ib le spectrum showed complete reaction. Amax: 435 (Soret)
and 575nm. The solvent was evaporated and the residue was redissolved
in acetone. The solution was filte re d and vapor diffused with pentane
to form square purple crystals. These were rinsed with pentane and
allowed to dry (0.27g, 37%). Anal. Calcd. for Cg6H64 N]o0 4 FeK: C,
68.55; H, 5.59; N, 12.12; Fe, 4.83. Found: C, 68.55; H, 5.56; N, 11.98;
Fe, 4.79. Mossbauer: (77K, 0G) 30%, 6=0.43mm/s and AEq=2.0mm/s; 70%,
6=0.20mm/s and AEq=0mm/s.
TFefPincerP) (CN) lE t> jN
Fe(PincerP)(THF) 2 (12mg, 0.08mmol) and Et4NC N (2mg, 0.12mmol) were
dissolved in THF (15mL) and stirred overnight. An orange precipitate
formed which was filte re d and dried (12mg, 98%). Amax: (THF) 428
(Soret) and 530nm. Mossbauer:(77K, 0G) 6=0.386mm/s and AEq=l.313mm/s.
IR: (KBr p e lle t) uCN at 2070cm"1.
114
Summary
Fe(PincerP)(THF) 2 has been synthesized and characterized. I t has
been oxidized to the fe rric complexes Fe(PincerP)OH and [Fe(PincerP) ] 2 0
which have been separated and pu rified. The ferrous porphyrin, its
carbon monoxide adduct, and the fe rric hydroxide have been combined
with various cuprous salts including copper(I) hexafluorophosphate,
copper(I) t r i f l a t e , copper(I) chloride, and copper(I) cyanide.
Reaction with the ferrous complex resulted in oxidation to F e ( III) as
well as the formation of 1:1 Fe/Cu complexes, however, structural
characterization was unsuccessful. In one case the ferrous porphyrin
remained in its Fe( I I ) oxidation state. The reaction of Fe(PincerP)
and CuCN in toluene resulted in an Fe( II)/C u complex, however,
dissolving this complex in THF resulted in a mixture of compounds.
115
References
1. Collman, J. P.; Gagne, R. R .; Reed, C. A.; Halbert, T. R .;
Lang, G.; Robinson, W . T. J. Am. Chem. Soc. 1975, 97, 1427-1439.
2. Rodgers, S. J .; Koch, C. A.; Tate, J. R.; Reed, C. A.;
Eigenbrot, C. W.; Scheidt, W . R. Inorg. Chem 1987, 26, 3647-3649.
3. Sams, J. R .; Tsin, T. B. In The Porphyrins; Dolphin, D., Ed.;
Academic: New York, 1979; Vol. 4, Chapter 9.
4. Chang, C. K.; DiNello, R. K .; Dolphin, D. In Inorganic Syntheses,
Busch, D. H., Ed.; John Wiley & Sons: New York, 1980; Vol XX,
pp 147-155.
5. English, D. R.; Hendrickson, W . N.; Suslick, K. S. Inorg. Chem.
1983, 22, 368-370.
6 . Reed, C. A.; Mashiko, T .; Bentley, S. P.; Kastner, M. E.;
Scheidt, W . R.; Spartalian, K.; Lang, G. J. Am. Chem. Soc. 1979,
101, 2948-2958.
7. Gupta, G. P.; Lang, G.; Scheidt, W . R .; Geiger, D. K .; Reed, C. A.
J. Chem Phys. 1986, 85, 5212-5220.
8 . Collman, J. P.; Brauman, J. I . ; Doxsee, K. M.; Halvert, T. R.;
Hayes, S. E.; Suslick, K. S. J. Am. Chem. Soc. 1978, 100, 2761-
2766.
9. Wuenschell, G. E. Ph.D. Thesis, University of Southern C alifornia,
November 1987.
10. Jameson, G. B.; Ibers, J. A. Comments Inorg. Chem. 1986, 97-126.
11. James, B. R. In The Porphyrins, Dolphin, D., Ed.; Academic:
New York, 1978; Vol. 5, Chapter 6 .
12. Gunter, M. J .; Mander, L. N.; Murray, K. S.; Clark, P. E.
J. Am. Chem. Soc. 1981, 103, 6784-6787.
13. Lexa, D.; Momenteau, M.; Saveant, J. M.; Xu, F. Inorg. Chem. 1985,
24, 122-127.
14. Woon, T. C.; Shirazi, A.; Bruice, T. C. Inorg. Chem. 1986, 25,
3845-3846.
15. Cheng, R. J .; Latos-Grazynski, L.; Balch, A. L. Inorg. Chem. 1982,
21, 2412-2418.
16. Gunter, M. J .; Mander, L. N.; Murray, K. S. J.C.S. Chem Commun.
1981, 799-801.
1 1 6
17. Gunter, M. J .; McLaughlin, G. M.; Berry, K. J .; Murray, K. S.;
Irving, M.; Clark, P. E. Inorg. Chem. 1984, 23, 283-300.
18. Cense, J. M.; Le Quan, R. M. Tetd. Letts. 1979, 39, 3725-3728.
19. Harel, Y.; Felton, R. H. J.C.S. Chem. Commun. 1984, 206-208.
20. Jayaraj, K.; Gold, A.; Toney, G. E.; Helms, J. H.; H atfield , W . E.
Inorg. Chem. 1985, 25, 3516-3518.
21. Miyamoto, T. K.; Tsuzuki, S.; Hasegawa, T .; Sasaki, Y.
Chem. Letts. 1983, 1587-1588.
22. Gordon, A. J .; Ford, R. A. The Chemists Companion; John Wiley &
Sons: New York, 1972; Chapter 4.
23. Scheidt, W . R.; H aller, K. J .; Hatano, K. J. Am. Chem. Soc. 1980,
102, 3017-1021.
24. Scheidt, W . R.; Lee, Y. J .; Luangdilok, W.; H aller, K. J .;
Anzai, K .; Hatano, K. Inorg. Chem. 1983, 22, 1516-1522.
25. Caughey, W . S. In Inorganic Biochemistry; Eichorn, G., Ed.;
Elsevier: Amsterdam, 1973; Vol. 2, Chapter 24.
26. Nyquist, R. A.; Kagel, R. 0. Infrared Spectra of Inorganic
Compounds, Academic: New York, 1971; pp 60-61.
27. Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 4th ed.; John Wiley & Sons: New York,
1986; pp 272-280.
28. Gunter, M. J .; Berry, K. J .; Murray, K. S. J. Am. Chem. Soc, 1984,
106, 4227-4235.
29. Morpurgo, G. 0 .; Mosini, V.; Porta, P.; Dessy, G.; Fares, V.
J. Chem. Soc., Dalton Trans. 1981, 111-117.
117
Chapter 5
Imidazolate Bridged Complexes
The success of pincer porphyrin's a b ility to serve as a
binucleating ligand has been demonstrated. However, there are
lim itations to this strategy, and in order to study Fe/Cu complexes of
a d ifferen t nature we turned our attention to an alternative approach.
This method consists of combining two preformed metal complexes, one
being a metal 1oporphyrin, and the other containing a ligand capable of
bridging, to form a bridged binuclear complex. The specific bridging
ligand of interest in this work is imidazolate.
As mentioned in Chapter 1, the presence of an imidazole ligand to
heme in the active site of cytochrome c oxidase has been shown in
EPR studies of the nitrosyl adduct of the fu lly reduced enzyme. 1 ’ 2
Assuming this imidazole is also present in the fu lly oxidized or
resting state of the enzyme, i t has been postulated that the EPR
118
silence of this form of the enzyme could be caused by strong a n ti
ferromagnetic coupling (-J>200cm"l) between the F e ( III) and Cu( I I )
sites fostered by an imidazolate bridge. 3
Model compounds aimed at testing this theory have been synthesized
in the form of homobinuclear complexes as well as heterobinuclear
complexes. Bis-copper imidazolate bridged complexes are numerous4 " 8
and show weak to moderate coupling with -J ranging from 0.5 - 90cm"l.
The homonuclear face-to-face porphyrins9 ’ 10 of M n(II) and F e (II)
exhibit weak anti ferromagnetic coupling with -J=2cm- ^.
H eterobinuclear im idazolate bridged compounds have been
synthesized by several groups10-17 and where magnetic data have been
obtained, i f anti ferromagnetic coupling was observed i t was weak at
best. For example, the M n (II)-Im -C o (II) moiety in face-to-face
porphyrin exhibits weak coupling (-J-5cm- ^ ) 10 while the F e (III)-Im -
C u (II) moiety found in Prosperi and Tomlinson's11 (TTP)Fe-(2-MeIm)-
Cu(acac)2 > where TTP is tetratolylmesoporphyrin, and in Wilson's15
Fe(UroTPP)Cu(acac)2 > where UroTPP is urocanyl tetraphenylporphyrin,
show no coupling of the metals. However, there are two apparent
exceptions to the rule that imidazolate can mediate only weak coupling.
These are both prepared by Wilson and co-w orkers, 1 6 ’ 17
[(TPP)Fe(imid}Cu]0 3 SCF3 and [(TPP)Mn(imid)Cu]0 3 SCF3 and combine an
im idazolate copper complex w ith an F e ( I I ) and a M n (II)
metalloporphyrin, respectively. In both cases the decrease in the room
temperature magnetic moment and the EPR silence was assumed to be due
to very strong anti ferromagnetic coupling with -J>200cm-1 . However,
this work fa ile d to resolve the question of the exact spin state of the
119
iron in the Fe/Zn analogue due to uninterpretable Mossbauer data, the
complexes are not completely ESR s ile n t, and the manganese complexes
show vis ib le spectra characteristic of M n (III) . 18 Therefore, the
interpretation of strong anti ferromagnetic coupling is premature.
Imidazolate has been proven as a bridging ligand capable of
'coupling two metals antiferrom agnetically, a lb e it generally weak to!
I ;
moderate coupling. Whether imidazolate is capable of fostering the,
strong (-J>200cm"l) coupling postulated in cytochrome c oxidase remains'.
| uncertain. Undoubtedly, further study of M-Im-M systems is necessary,'
I I
especially concerning iron/copper systems, in order to fu lly understand'
i i
! the v ia b ility of imidazolate as a ligand capable of strongj
, anti ferromagnetic coupling and as a potential bridge in the cytochrome1
i c oxidase active s ite .
The metal imidazolate complexes used in this work have beenj
synthesized previously19 and are formed from the condensation of 5-
chloro-2-hydroxybenzophenone, o-phenylenediamine, and im idazole-4(5)-
carboxaldehyde. The copper(II) and n ic k e l(II) complexes (abbreviated,
Culm and Nilm, respectively) were supplied by Prof. Greg Brewer at The
Catholic University of America in Washington, D. C.
Combination of these imidazolate complexes with metalloporphyrins
; has been achieved prior to this work including the reactions with
i
CoTPP20 and ZnTPP. 21 The cobalt porphyrin proved the a b ility of the
metal imidazolate complexes to bind a metalloporphyrin as evidenced by
the d is tin c tiv e ESR spectrum of Co(TPP)(NiIm). The zinc porphyrin was
used to measure the equilibrium constants of the reactions. The
's im ila rity between the changes in the v is ib le spectrum of Zn(TPP) upon
binding 1 -methyl imidazole and the copper and nickel imidazolate
complexes also indicated that MIm acts as a neutral donor in contrast
to imidazolate. No magnetic studies of these metalloporphyrin metal,
imidazolate complexes have been conducted as yet. ;
(
In th is work, the nickel and copper imidazolate complexes were
reacted with ir o n ( II) , ir o n ( I I I ) , and manganese(II) prophyrins and the
magnetic properties of these compounds were measured. The compounds
in c lu d e copper and n ic k e l analogues o f Fe(TPP) (MIm)2 »
[Fe(TPP)(MIm)2 ](B 11CH12), Mn(TPP)(MIm), and [Fe(C2Cap)(MIm)](B11CH12) ,
where M = Cu or Ni and C2Cap = Baldwin's capped porphyrin. The
diamagnetic nickel analogue is used to produce magnetic blanks of each
compound and therefore characterize the magnetic properties of the
metalloporphyrins in the absence of a second magnetically interacting
metal. Synthesis of these compounds consisted of dissolving each
— N
Ci
M * N i, Cu
Figure 5-1. Schematic drawing of metal imidazolate complexes
where M * = Cu, Ni.
121
metalloporphyrin in either THF or toluene, adding the appropriate
imidazolate complex, and c rys tallizin g by vapor diffusion of heptane.
The compounds were characterized by th e ir v is ib le spectra and elemental
analyses. Variable temperature magnetic susceptibilities were measured
fo r each compound and Mossbauer spectra were obtained on ^ F e enriched
samples of the iron complexes.
Experimental
All reactions were conducted in a helium f ille d in ert atmosphere
glove box from Vacuum Atmospheres. The oxygen level was maintained at
less than lppm re la tiv e to a 5% hydrogen in nitrogen forming gas.
Tetrahydrofuran (THF), toluene, and heptane were d is tille d from
sodium/benzophenone. Dimethylformamide (DMF) was d is tille d from barium
oxide under vacuum.
Absorption spectrum were recorded on a Shimadzu UV260
spectrophotometer. Elemental analyses were performed at the University
of C alifornia, Berkeley, Microanalytical Laboratory. Mossbauer
analyses were performed on samples embedded in paraffin wax by Dr.
Gupta Govind in Prof. George Lang's group at Penn State University,
Philadelphia, Pennsylvania.
Mn(TPP)-2toluene and Mn(TPP)(l-Melm)-0.08THF have been prepared
previously. 22-24 Fe(TPP)(THF)2 has been synthesized previously, 25 but
i t was prepared in this work using the ferrous bromide procedure
presented in Chapter 4. Fe(TPP)(B11CH12 ) ‘C7H3 has been prepared
previously26 but in this work the reaction was performed in THF to form
Fe(TPP)(B]]CHj2 )-2THF. F e ^C ap ) has been prepared previously, 2 7 * 28
1 2 2
and again the ferrous bromide method was used to form Fe(C2Cap)(THF).
Variable temperature magnetic data were collected on powdered
samples in a precalibrated aluminum bucket using an S.H.E. Corporation
900 Series VTS SQUID susceptometer. The gram su sceptibility, Xg> of
the sample at each temperature was calculated using,
Xa = Msamp - Mbuc
y g x H
where Msamp is the measured magnetization of the sample and bucket,
Mbuc is the magnetization of the empty bucket, g is the weight of the
sample in grams, and H is the magnetic fie ld in gauss.
The molar suscep tibility, xm> ° f the sample at each temperature
was calculated using,
XM = Xg * M W - (Xdia + TIp)
where M W is the molecular weight, Xdia the diamagnetic correction
tabulated from Pascal's constants29’ 30 (in the case of H2TPP, the
experimental value of -700x10"® emu/mol was used31), and TIP is the
temperature independent paramagnetism. TIP values for each complex
were used as f o l l o w s : Nilm, Mn( TPP) ( NiIm) , and
[Fe(C2Cap)(NiIm)](B11CH12 ), TIP=90xl0"6emu/mol; Culm, Mn(TPP)(Culm),
and [Fe(C2Cap)(CuIm)](B11CH12), TIP=60xl0"6emu/mol; Fe(TPP)(Culm)2,
TIP=250xl0"®emu/mol; Fe(TPP)(NiIm)2 * TIP=370xl0~®emu/mol;
[Fe(TPP)(NiIm)2 ](B n CH12), TIP=620xl0"6emu/mol;
[Fe(TPP) (Culm)2] (BnCH12) , TIP=300xl0"6emu/mole.
The effective magnetic moment, Meff> at each temperature was
calculated using,
(leff - 2.828(xHT )V 2
123
The g values for the paramagnetic and coupled systems were
calculated from the 1 / xm v s . T plots using Curie law ,30
g2 = 3km/N/?2S(S+l)
where k is the Boltzman constant, N is Avogadro's number, p is the Bohr
magneton, m is the inverse slope of the 1 / xm v s . T p lo t, and S is the
spin quantum number.
The values of g, D, the zero fie ld s p littin g , and J, the magnetic
coupling constant, for the magnetically coupled systems were obtained
using a non-linear least squares program supplied by Prof. Peter D. W .
Boyd at University of Auckland, New Zealand.
Fe(TPP)(NiIm)2.2toluene
Fe(TPP)(THF) 2 (0.050g, 0.062mmol) was dissolved in hot toluene
(25mL) and filte re d . Nilm (0.056g, 0.122mmol) was dissolved in hot
toluene (25mL) and added to the metal!oporphyrin solution. I t was then
heated for 5min and allowed to cool and c ry s ta llize overnight. Large
cubic crystals formed which were filte re d and rinsed with heptane
(0.075g, 70%). Anal. Calcd. for C9oH58N1202Cl2FeNi2 ’ 2C7H8 : C, 70.64;
H, 4.23; N, 9.51; Fe, 3.20; Ni, 6.31. Found: C, 70.79; H, 4.40; N,
9.61; Fe, 3.16; N i, 6.64. Amax (toluene): 427 (Soret), 533, and 565nm.
Mossbauer (4.2k, 0G): 6=0.45mm/s and AEg=0.89mm/s.
Fe(TPP)(CuIm)2.2toluene
Fe(TPP)(THF)2 (0 .1 2g, 0.15mmol) was dissolved in hot toluene
(40mL) and filte r e d . Culm (0.14g, 0.30mmol) was dissolved in hot
toluene (40mL) and added to the metal 1oporphyrin solution. I t was then
124
heated for 5min and allowed to cool and c ry s ta lliz e overnight. Large
cubic crystals formed which were filte re d and rinsed with heptane
( 0 .13g, 50%). Anal. Calcd. for CggHggN^C^C^^Fe^CyHg: C, 70.26; H,
4.20; N, 9.46; Cu, 7.15; Fe, 3.14. Found: C, 70.04; H, 4.41; N, 9.65;
Cu, 7.11; Fe, 3.10. Amax (toluene): 428 (Soret), 535, and 566nm.
Mossbauer (4.2K, 0G): 6=0.45mm/s, AEg=0.89mm/s and S=0.55mm/s,
AEq=1.47mm/s.
rFe(TPP)(N1Im)2IXBl l CHi2),.5THF
Fe(TPP) (Bn CH12)(THF)2 (0.02g, 0.02mmol) and Nilm (O.Olg,
0.02mmol) were dissolved in hot THF (15mL) and filte r e d . Heptane (2mL)
was added and heptane was allowed to diffuse into the solution. After
several days, dark crystals formed which were filte re d and rinsed with
heptane (0.022g, 53%). Anal. Calcd. for C g iH jg N ^ ^ B llC ^ F e l^ 'S C ^ g O :
C, 63.87; H, 5.31; N, 8.05; Fe, 2.68; N i, 5.62. Found: C, 57.98; H,
4.97; N, 8.41; Fe, 2.95; Ni, 5.56. Amax (THF): 417 (Soret) and 446nm.
Mossbauer (77K and 4.2K, 0G): 5=0.24mm/s and AEq=2.26mm/s.
rFefTPPHCuImlgH B ! jCHj ?1.5THF
Fe(TPP)(BjjCHj2)(THF)2 (0.036g, 0.038mmol) was dissolved in THF
(20mL). Culm (0.045g, 0.097mmol) was added and the solution was heated
for 2min. I t was then filte re d to separate a small amount of insoluble
precipitate. Heptane was allowed to diffuse into the solution to
p re c ip ita te the product (0.069g, 88%). Anal. Calcd. for
^91^70^12^2^11^^2^u2^e‘ ^^4^8^: 63.57; H, 5.29; N, 8.02; Cu, 6.06;
Fe, 2.67. Found: C, 63.28; H, 5.29; N, 8.08; Cu, 6.31; Fe, 2.47.
125
Amax (THF): 417 (Soret), 548, and 582nm. Mossbauer (77K and 4.2K,
OG): 6=0.23mm/s and AEQ=2.07mm/s. X-ray quality crystals were grown by
toluene diffusion into a concentrated DM F solution.
Mn(TPP)(NiIm).3toluene
Mn(TPP)-2toluene (0.052g, 0.061mmol) and Culm (0.030g, 0.066mmol)
were dissolved in toluene (15mL). The solution was heated for 2min,
then filte re d and diffused with heptane. Very large dark crystals
formed a fte r several days. These were filte re d and rinsed with heptane
(0.026g, 31%). Anal. Calcd. for C67H43N8OClMnNi-3C7H8 : C, 75.40; H,
4.83; n, 8.00; Mn, 4.19; Ni, 3.92. Found: C, 75.23; H, 5.01; N, 8.56;
Mn, 3.75; N i, 4.53. Amax (toluene): 417, 440 (Soret), 533, 575, 616,
and 652nm.
Mn(TPP)(Culm).toluene
Mn(TPP)-2toluene (0.13g, 0.015mmol) and Culm (0.077g, 0.017mmol)
were dissolved in hot toluene (lOmL). The solution was filte re d and
diffused with heptane to form dark hexagonal crystals. These were
filte re d and rinsed with heptane (0.10g, 52%). Anal. Calcd. for
c67H43N80C1CuMn’ c7H8 : c > 72.71; H, 4.21; N, 9.17; Cu, 5.20; Mn, 4.49.
Found: C, 71.62; H, 4.77; N, 9.21; Cu, 5.18; Mn, 4.11. Amax (toluene):
417, 442 (Soret), 535, 576, 617, and 652nm.
Fe(C2Cap)fB1 ^CH^) .2THF
Fe(C2Cap)Cl (0.40g, 0.355mmol) was dissolved in THF (25mL).
AgBuCH^ (0.10g, 0.399mmol) was dissolved in benzene (25mL) and added
1 2 6
to the metal 1oporphyrin solution. I t was stirred lh r, then filte re d to
remove the s ilv e r chloride. Heptane was allowed to diffuse into the
solution to form long needle-like crystals of the bis-THF adduct.
These were filte re d and rinsed with 1:1 benzene/heptane(0.41g, 84%).
Anal. Calcd. fo r C63H54N4 0 12 B i1Fe*2C4H 8 0 : C, 61.87; H, 5.14; N, 4.07.
Found: C, 61.38; H, 5.16; N, 3.80.
rFefCgCapHNilmllfB! i CH12).4THF
FefCgCap)(BiiCHjg)'2THF (0.086g, 0.062mmol) was dissolved in THF
(15mL) and Nilm (0.030g, 0.066mmol) was added. The solution was heated
for 2min then filte re d . Heptane (3mL) was added and the solution
diffused with heptane. Light brown clusters formed a fte r several days
which were filte re d and rinsed with heptane (O.lOlg, 79%). Anal. Calcd.
for C 8 5 H6 9N8 0 13 B11ClFeNi*4 C4H8 0 : C, 62.04; H, 5.37; N, 5.46; Fe, 2.72;
Ni, 2.86. Found: C, 58.98; H, 5.24; N, 5.29; Fe, 2.61; Ni, 2.52. Amax
(THF): 412 (Soret) and 512nm. Mossbauer (4.2K, 0G): S=0.27mm/s and
AEq=2.47mm/s.
rFefCgCapHCuImlKB! i C H j 2).THF
Fe(CgCap)(BjiCHjg)'2THF (0.098g, 0.071mmol) was dissolved in hot
THF (15mL) and Culm (0.033g, 0.070mmol) was added. The solution was
heated for lmin then filte re d . Heptane (2mL) was added and the
solution was diffused with heptane. A c rys tallin e product formed over
several days and was filte re d and rinsed with heptane (0.108g, 86%).
Anal. Calcd. for C85HggN80j3BjiClCuFe*C4H80: C, 61.12; H, 4.39; N,
6.34; Cu, 3.59; Fe, 3.16. Found: C, 60.62; H, 4.56; N, 6.16; Cu, 3.40;
127
Fe, 3.15. Amax (THF): 413 (Soret), 512, and 578nm. Mossbauer j
S
(77k, OG); 36%, 5=0.40mm/s and AEq=2.41mm/s; 64%, 5=0.39mm/s and
|AEq= 1.20mm/s. (4.2k, OG): 38%, 5=0.36mm/s and AEq=2.50mm/s; 62%,
5=0.40mm/s and AEq=l. 20mm/s. i
■ i
I |
[Results I
i :
Metal Imidazolate Complexes 1
i
j The Nilm complex exhibits a room temperature magnetic moment o f 1
i i
0.25fiQ indicating low-spin nickel ( I I ) as expected for a square planar
d8 configuration. The small deviation from diamagnetism, presumably
'caused by paramagnetic im purities, could not be avoided even with'
I
repeated crys ta lliza tio n s . This is consistent with the magnetic
studies on nickel complexes of sim ilar symmetrical Schiff bases in
which paramagnetic impurities were unavoidable.19 Table 5-1 gives the
variable temperature magnetic data, and Figure 5-2 plots the magnetic
moment vs. temperature for 6 to 300K.
The Culm complex is associated in pairs exhibiting a small
anti ferromagnetic coupling between the copper atoms. This is
demonstrated by the decrease in the magnetic moment at low temperature
.(Figure 5-3 ). The magnetic moment has been calculated per "dimeric"
|(CuIm)2 in order to calculate a coupling constant, J, and to compare
the data to the iron porphyrin bis-imidazolate complexes which contain,
two copper atoms. The moment remains at =2.46/zg from 300 to 75K then
gradually decreases to 2.36/xg at 20K then decreases sharply to 2.20ij%
i
by 6K. The best theoretical f i t shown by the solid curve gives g=2.02:
and_J=-l.61cnrl, The change in the__recip_rocal molar susceptibility as J
, BM
1 . 0 0
0 .7 5 -
0.50
0.25
................
0.00
0 25 50 75 100 125 150 175 200 225 250 275
Temperature, K
Figure 5-2. Plot of effective magnetic moment vs. temperature for Nilm.
n o
00
TEMP MAGSN. CORR. CH IG CHIM MUEFF 1 /C H IM
129
6.00000 1 .5 5 1 186-03 1.21187E-03 1 .05048E-06 6 . 08682E-04 0.17090
\642•89283
7.00166 1.50671E-03 1.20954E-03 9.20012E-07 5.48979E-04 0.17533
1821.56274
8.00000 1.46791E— 03 1.20950E-03 8.00000E-07 4.94064E-04 0.17779
2024.02916
10.00166 1.4 1 295E-03 1.20504E-03 6.43668E-07 4.22529E-04 0.18384
2366.69779
12.00000 1.37540E-03 1.20374E-03 5.31424E-07 3.71169E-04 0.18873
2694.18997
14.99500 1.33295E-03 1.19921E-03 4.14046E-07 3.17459E-04 0.19311
3150.01123 .
19.99833 1 . 28768E-03 1.19922E-03 2.73839E-07 2.53303E-04 0.20127
3 9 4 7 83672
25.00000 1.25895E-03 1.19884E-03 1.86069E-07 2.13141E-04 0.20643
4691.71234
29.99666 1.23876E-03 1.19613E-03 1.31979E-07 1.88391E-04 0.21259
5308.10688
34.99500 1 . 22086E-03 1.19461E-03 8.12665E-08 1.65185E-04 0.21501
6053.78403
39.98333 1.20820E-03 1.19335E-03 4.59635E-08 1.49032E-04 0.21830
6709.96742
44.97833 1 . 19933E-03 1.19178E-03 2.33656E-08 1.38691E-04 0.22336
7210.23810
50.09500 1 .1 8883E-03 1.19167E-03 -8.81962E-09 1 . 23964E-04 0.22285
8066.83768
55.21333 1.18191E-03 1.18897E-03 -2.18677E-08 1.17993E-04 0.22826
8475.02551
60.29500 1 .17713E-03 1 .1 8786E-03 -3.32289E-08 1 .1 2795E-04 0.23321
8865.63240
65.00500 1 .1 6905E-03 1.18627E-03 -5.33348E-08 1.03595E-04 0.23207
9652.97236
69.98333 1.16320E-03 1.18457E-03 -6.61919E -08 9.77119E-05 0.23385
10234.16780
75.11666 1 .1 5735E-03 1.18256E-03 -7.80770E-08 9.22735E-05 0.23544
10837.34600
80.35000 1.15101E-03 1.18069E-03 -9.19160E-08 8.59410E-05 0.23500
11635.88350
90.81666 1.14136E-03 1 .1 7625E-03 -1.08045E-07 7.85606E-05 0.23887
12729.02600
99.95000 1.13345E-03 1.17250E-03 -1.20927E-07 7.26661E-05 0.24101
13761.55950
110.06666 1 .1 2466E-03 1.16370E-03 -1.20895E-07 7.26805E-05 0.25293
13758.84230
120.65000 1.11520E-03 1.16022E-03 -1.39401E-07 6.42124E-05 0.24891
15573.30590
130.56666 1.10438E-03 1.15407E-03 -1.S3866E-07 5.75939E-05 0.24523
17362.94300
140.28333 1.09818E-03 1.14903E-03 -1.57431E-07 3.59624E-05 0.25057
17869.12190
161.28333 1.08123E-03 1.13442E-03 -1.64677E-07 5.26469E-05 0.26059
18994.45980
180.06666 1.06521E-03 1.12331E-03 -1.79883E-07 4.56888E-05 0.25650
21887.19060
201.35000 1.04691E-03 1.10391E-03 -1.76491E-07 4.72409E-05 0.27581
21168.07940
221.16666 1 . 02725E-03 1.09199E-03 -2.00441E -07 3.62821E-05 0.25332
27561.76930
240.95000 1.01048E-03 1.07784E-03 -2.08547E-07 3.25729E-05 0.25053
30700.29150
260.75000 9.93483E— 04 1.05911E-03 -2.03201E-07 3.50190E-05 0.27023
28555.88600
280.43333 9.78150E-04 1.04949E-03 -2.20890E-07 2.69250E-05 0.24573
37140.06900
Mass oi samp 1*Molecular Weight » 457.58000
Diamagnetic c o r r t c t i o n / T l P <«E- 6 ) “ -128.00000
Table 5-1. Variable temperature magnetic su sceptibility data fo r Nilm
in 10KG magnetic fie ld . TEMP=temperature, K; MAGSN=magnetization of
sample and bucket; CORR=magnetization of bucket; CHIG=gram suscep
t i b i l i t y ; CHIM=molar susceptibility; MU£FF=effective magnetic moment;
and l/CHIM=reciprocal molar susceptibility.
400
3.0
3 0 0 -
^ 2 0 0 -
100 -
0 25 50 75 100 125 150 175 200 225 250 275 300
Temperature, K
Figure 5-3. Plots of reciprocal molar susceptibility and effective magnetic moment vs.
temperature for (Culm)2 . For 1/xm (triangles) vs. T, solid line is linear least-squares f i t with
slope - 1.295, x-intercept ■ -2.02, and coefficient of correlation = 0.99998. For /ief f (circles)
vs. T, curve is theoretical f i t with g = 2.02 and 0 = -1.61cm- ^.
O S I
TEMP MAGSN. CORR. CHIG CHIM MUEFF 1 /C H IM J 3 ]
<4.00000 0.02976 1.211G7E-03 I.08548E-04 0.10070 2.19823 9.93026
7.00000 0.02645 1.20954E-03 9.59713E-05 0.08907 2.23304 11.22697
8.00000 0.02383 1.20950E-03 8.60094E-05 0.07985 2.26039 12.52216
10.00000 0.01986 1.20504E-03 7.09313E-05 0.06591 2.29598 15.17127
11.99500 0.01706 1.20 375E-03 6.02899E-05 0.05607 2.31929 17.83398
15.00000 0.01413 1.19920E-03 4.91665E-05 0.04578 2.34363 21 .84089
20.00000 0.01102 1.19922E-03 3.73413E-05 0.03484 2.36098 28.69470
25.00000 9 .1 4566E-03 1.19884E-03 3.02160E-05 0.02826 2.37703
35.38561
29.99833 7.89250E-03 1.19613E-03 2.54614E-05 0.02386 2.39271
41.90581
34.99666 6.99016E-03 1.19461E-03 2.20363E-05 0.02069 2.40674
48.31991
39.99833 6.29633E-03 1.19334E-03 1.94029E-05 0.01826 2.41685
54.76433
44.99333 5.75366E-03 1.19178E-03 1.73455E-05 0.01635 2.42610
61.13464
50.01500 5 .3 1 650E-03 I.19169E -03 1.56836E-05 0.01482 2.43477
67.47455
55.27833 4.93616E-03 1.18894E-03 1.42479E-05 0.01349 2.44233
74.11443
60.37333 4.62183E-03 1.18784E-03 1.30569E-05 0.01239 2.44601
80.70219
64.99833 4.38516E-03 1.18627E-03 1.21630E-05 0.01156 2.45185
86.47149
70.00000 4.14916E-03 1.18457E-03 1.12721E-05 0.01074 2.45212
93.10437
75.35000 3 . 93050E-03 1.18248E-03 1.04487E-05 9.979O9E-03 2.45226
100.20944
80.40000 3 . 75083E-03 1.18067E-03 9.77243E-06 9.35364E-03 2.45243
106.91020
90.00000 3 . 47783E-03 1.17660E-03 8.74991E-06 8.40800E-03 2.46006
118.93427
99.91666 3 . 24566E-03 1.17252E-03 7.88262E-06 7.60592E-03 2.46532
131.47637
110.86666 3.02616E-03 1.16323E-03 7.08338E-06 6.86678E-03 2.46749
145.62859
120.15000 2.85833E-03 1.16044E-03 6.45583E-06 6.28642E-03 2.45778
159.07297
130.56700 2.69830E-03 1 .1 5407E-03 5.87156E-06 5.74608E-03 2.44952
174.03164
140.15000 2 . 60200E-03 1.14910E-03 5.52431E-06 5.42493E-03 2.46588
184.33387
161.48300 2 . 38050E-03 1.13429E-03 4.73843E-06 4.69814E-03 2.46323
212.84975
180.01700 2.24120E-03 1.12334E-03 4.25038E-06 4.24679E-03 2.47267
235.47168
200.00000 2 . 10600E-03 1.10491E-03 3.80639E-06 3.83619E-03 2.47710
260.67494
219.96700 1 . 99300E-03 1.09277E-03 3.42289E-06 3.48153E-03 2.47481
287.23003
239.90000 1.89780E-03 1.07873E-03 3.11431E-06 3.19614E-03 2.47632
312.87681
259.90000 1.81196E-03 1.05970E-03 2.86028E-06 2.96121E-03 2.48094
337.69899
279.85000 1.73591E-03 1.04989E-03 2.60840E-06 2.72827E-03 2.47107
366.53166
299.80000 I.67050E-03 1.03241E-03 2.42618E-06 2.55975E-03 2.47739
390.66200
Maas of sainpletgrams) * 0.02630
Molecular Weight = 924.81000
i Diamagnetic c o r re c tio n /T IP <*E - 6 > « -316.00000
Table 5-2. Variable temperature magnetic susceptibility data for
(Culm)2 in 10K6 magnetic fie ld . TEMP=temperature, K; MAGSN=magne-
tiza tio n of sample and bucket; C0RR=magnetization of bucket; CHIG=gram
su sceptibility; CHIM=molar susceptibility; MUEFF=effective magnetic
moment; and l/CHIM=reciproca1 molar su sceptibility.
132
a function of temperature is also shown in Figure 5-3. This shows the
Curie-Weiss behavior of the complex with a small negative intercept,
$=-2.02°, indicative of anti ferromagnetic coupling. These magnetic
data are consistent with the crystal!ographic investigation by Brewer
and Sinn20 in which they observed dimerization of Culm. The variable
temperature data for (Culm)2 is shown in Table 5-2.
Ir o n (II) Bis-Metal Imidazolate Complexes
Fe(TPP)(NiIm)2 showed essentially diamagnetic behavior. The
ir o n (II) center is forced into the low spin, S=0, configuration due to
the presence of bis-imidazole ligands as in Fe(TPP)(1-Melm)2.33 Like
the simple nickel imidazolate complex, paramagnetic impurities could
not be avoided. Figure 5-4 plots the magnetic moment vs. temperature
from 6 to 300K. I t remains essentially constant at =0.5/zb until low
temperature where a slight decrease occurs which may be due to the
impurities. Table 5-3 gives the variable temperature magnetic data.
The 4.2K Mossbauer parameters for this complex were consistent with
low spin ir o n (II) with 6=0.45mm/s and AEQ=0.89mm/s. These parameters
are sim ilar to those of Fe(TPP)(HIm)2 , where Him = imidazole, with
5=0.45mm/s and AEq=1.06mm/s.34
Fe(TPP)(Culm)2 displayed magnetic behavior very sim ilar to the
"dimeric" (Culm)2 , but with a s lig h tly weaker anti ferromagnetic
coupling between the copper atoms. The room temperature magnetic
moment was somewhat higher at 2.61 fiQ (Figure 5 -5 ), but i t remained
constant to 75K then gradually decreased until 6K where i t decreased
sharply. The best theoretical f i t gave g=2.11 and J=-0.74cm'l. As in
133
(Culm)2 > the 1 / xm v s . temperature plot shows Curie-Weiss behavior with
a small negative intercept, 0=-1.25°. The variable temperature
magnetic data is shown in Table 5-4. The 4.2K Mossbauer spectrum for
this sample contained one low spin ir o n (II) component with 5=0.45mm/s
and AEg=0.89mm/s, and a second apparently intermediate spin ir o n (II)
component with 6=0.55mm/s and AEq=1.47mm/s, which is possibly starting
m a te ria l. (Compare Fe(TPP)• 2toluene w ith 6=0.52mm/s and
AEq=1.51mm/s.35)
Ir o n fU P Bis-Metal Imidazolate Complexes
The magnetic p ro p ertie s of [Fe(TPP) (Ni Im)2 ] (Bj 1CH2 2 ) are
straightforward. The ir o n ( III) center is low spin, S =l/2, due to the
strong fie ld imidazole ligands. The room temperature magnetic moment
at 2.10/zg (Figure 5-6) is s lig h tly higher than the spin only value of
1.73/ig, but not atypical of low spin fe rric porphyrins. Table 5-5
gives the variable temperature magnetic data. The g value calculated
from the 1 / xm v s . T plot is 2.42, s lig h tly higher than typical values
for low spin i r o n ( I I I ) . 36 The variable temperature magnetic data is
shown in Table 5-5. The Mossbauer parameters of this complex were
typical of low spin ir o n ( III) with 5=0.24mm/s and AEq=2.26mm/s.
(Compare the 77K Mossbauer parameters of [Fe(TPP)(HIm)2 ]Cl with
5=0.23mm/s and AEq=2.23mm/s.34)
The [Fe(TPP)(Culm)2 l(B ijC H i2 ) molecule is a unique species in
that i t is the f ir s t complex fo r which the imidazolate bridge mediates
ferromagnetic coupling rather than anti ferromagnetic coupling of the
metal centers. The ir o n ( III) center is again low spin, so that there
2 . 0
2
C D
0 .5 -
0.0
0 25 50 75 100 125 150 175 200 225 250 275 300
Temperature, K
Figure 5-4. Plot of effective magnetic moment vs. temperature for Fe(TPP)(NiIm)2 -2toluene.
to
TEMP MAGSN. CORR. CH IG CHIM MUEFF 1/C H JM
135
6.00000 1.94670E-03 1.23921E-03 1.74256E-06 3.80594E-03 0.42735
262.74691
6.9 76 6 6 I .87316E-03 I.23320E-03 1.57624E-06 3.5I18 7 E -0 3 0.44266
284.74778
7.99000 1 .80833E-03 1.22884E-03 1.42730E-06 3.24854E-03 0.45561
307.82965
10.01000 1.69400E-03 1.22S90E-03 1.1S295E-06 2.76348E-03 0.47035
361.86243
12.00000 1.61880E-03 I.22425E-03 9.71793E-07 2.44317E-03 0.48422
409.30269
15.00000 1.52480E-03 1.22386E-03 7.41230E-07 2.03553E-03 0.49415
491.27212
20.00500 1.41300E-03 I.21987E-03 4.75678E-07 1.56602E-03 0.50055
638•55995
23.00333 I .34971E-03 1.21722E-03 3.26305E-07 1.30192E-03 0.51023
768.09377
29.99333 1.30471E-03 1.21611E-03 2.18223E-07 1.11082E-03 0.51619
900.22838
35.00000 1.26856E-03 1.21282E-03 1.37268E-07 9.67697E-04 0.52045
1033.38057
39.99166 1.24563E-03 1.21000E-03 8.77544E-08 8.80154E-04 0.53057
1136.16451
44.98833 I.22505E-03 1.20940E-03 3.85462E-08 7.93151E-04 0.53420
1260.79298
50.15833 1 . 20655E-03 1.20924E-03 -6.64369E-09 7.13253E-04 0.53490
1402.02584
55.25333 1.1P100E-03 1.20814E-03 -4.22395E -08 6.50318E-04 0.53607
1537.70851
60.35333 1.17685E-03 1.20424E-03 -6.74795E -08 6.05692E-04 0.54069
1651.00192
65.00000 1.16360E-03 I.20424E-03 -1.00122E -07 5.47977E-04 0.53372
1824.89106
70.00000 1.15533E-03 1.20346E-03 -1.18559E-07 5.15381E-04 0.53714
1940.31131
75.21666 1.14285E-03 1.20106E-03 -1.43380E -07 4.71495E-04 0.53256
2120.90977
80.40000 1.13560E-03 1.19802E-03 -1.53765E-07 4.53135E-04 0.53978
2206.84610
90.90000 1.12246E-03 1.19061E-03 - 1 .67876E-07 4.28185E-04 0.55792
2335.43440
99.91666 1.11003E-03 1.18812E-03 -1.92364E-07 3.848S9E-04 0.55458
2598.14536
110.40000 1 .09600E-03 1.18380E-03 -2.16274E-07 3.42616E-04 0.55000
2918.71809
120.73333 1.08648E-03 1.17724E-03 -2.23550E-07 3.29751E-04 0.56426
30 32•58657
130.23333 1.07471E-03 1.17349E-03 -2.43302E-07 2.94829E-04 0.55414
3391.79165
140,51666 1.06170E-03 1.16552E-03 -2.S5720E-07 2.72873E-04 0.55376
3664.70332
161.56666 1 .04368E-03 1.15082E-03 -2.63912E -07 2.S8389E-04 0.57782
3870.12848
180.01666 1 .02453E-03 1 .1 3982E-03 -2.83966E -07 2.22932E-04 0.56652
4485.66348
200.00000 1 .00251E-03 1.12640E-03 -3.05172E-07 1.85439E-04 0.54462
5392.58100
219.95000 9 . 8 7 7 16E-04 1 .1 1040E-03 -3 .0 2 2 0 IE -0 7 1.90691E-04 0.57917
5244.06139
239.91666 9.65066E-04 1.09452E-03 -3.18860E-07 1.61239E-04 0.55621
6201.96123
259.90000 9.49633E-04 1 .0 7868E-03 -3.17862E -07 1.63003E-04 0.58207
6134.85265
279.86666 9.31600E-04 1 .06430E-03 -3.26863E -07 I.47088E-04 0.57377
6798.61523
299.81666 9 . 1 6083E-04 1 .0 4677E-03 -3.21913E -07 1.5S841E-04 0.61129
6416.79590
Mass o-f samp 1 #M olecular Weight - 1768.05000
Diamagnetic c o r re c tio n /T IP (»E - 6 > “ -725.00000
Table 5-3. Variable temperature magnetic susceptibility data for
Fe(TPP)(NiIm)?*2toluene in 10KG magnetic fie ld . TEMP-temperature, K;
MAGSN=magnetization of sample and bucket; CORR=magnetization of buc
ket; CHIG=gram susceptibility; CHIM=molar susceptibility; MUEFF=eff-
ective magnetic moment; and 1/CHIM-reciprocal molar su sceptibility.
400 3.0
3 0 0 -
100 —
0 25 50 75 100 125 150 175 200 225 250 275 300
Temperature, K
Figure 5-5. Plots of reciprocal molar susceptibility and effective magnetic moment vs. temp
erature for Fe(TPP)(CuIm)2-2toluene. For 1/xm (triangles) vs. T, solid line is linear least-
squares f i t with slope = 1.175, x-intercept = -1.25, and coefficient of correlation = 0.99997
For (ief f (circles) vs. T, curve is theoretical f i t with g = 2.11, D = 0.01, and J = -0.74cm"*
T e m p m a g s n . c o r r . c m ig c h im h u e f f i / c h im
2 .0 800 0 0 .0 3 9 4 2 1 .23 385 E -03 I .36477E -04 0 .2 7 9 0 7 2 .1 3 4 4 4 3 .3 8 3 2 0
3.0 200 0 0 .0 4 7 3 2 1.2 3 1 7 1 E -0 3 1.23507E -04 0 .2 2 0 4 4 2 .3 0 7 3 7 4 .3 3 3 8 0
3 .7 0 0 0 0 0 .0 4 0 7 4 I.2 4 9 6 3 E -0 3 1 .05872E -04 0.1 891 1 2 .3 6 3 4 2 3 .2 8 7 7 2
3 .2 6 0 0 0 0 .0 3 0 9 9 1 .2 4 3 I3 E -0 3 7.9 7 3 0 3 E -0 3 0 .1 4 2 6 7 2 .4 4 9 9 2 7.0 087 1
6 .0 0 0 0 0 0 .0 2 8 2 3 1 .2 3 9 2 2 E -0 3 7 .2 4 I4 9 E -0 3 0 .1 2 9 6 3 2 .4 9 4 1 3 7.71371
7 .0 0 1 6 6 0 .0 2 4 2 3 1 .2 3 3 0 7 E -0 3 4 .1 7 0 7 3 E -0 3 0 .1 1 0 6 0 2 .4 8 8 6 6 9 .0 4 1 2 3
8 .0 0 0 0 0 0 .0 2 1 S 4 I .2 2 8 8 0 E-0 3 3 .4 307 2E -03 0 .0 9 7 8 0 2.30131 10.22431
10 .006 66 0 .0 1 7 6 0 1.22S 90E -03 4 .3 8 9 8 3 E -0 3 0 .0 7 8 9 4 2 .5 1 3 3 3 12 ,6 6 7 1 3
12 .001 66 0 .0 1 4 7 7 1 .2 2 423 E -03 3 .6 313 6E -03 0 .0 6 5 4 6 2.3 067 0 1 3 .2 7 3 4 6
14 .998 33 0 .0 1 2 0 9 I.2 2 3 8 6 E -0 3 2 .9 131 7E -03 0 .0 5 2 4 9 2 .5 1 4 0 7 18 .9 7 7 7 2
19 .998 33 9 .3 3 1 83E -03 1 .2 198 7E -03 2 .1 8 0 I4 E -0 5 0 .0 3 9 4 4 2 .5 1 8 6 2
23 .212 96
2 3 .0 0 1 6 4 7 .7 3 3 0 0 E -0 3 1 .2 1 7 2 3 E -0 3 1 .7 4 6 8 5 E -0 3 0 .0 3 1 9 3 2.52791
31 .289 73
3 0 .0 0 3 3 3 6 .6 5 7 3 0 E -0 3 1 .2 1 6 1 0 E -0 3 1.4S881E -0S 0 .0 2 6 8 3 2 .3 3 7 7 3
37.23941
3 4 .9 9 3 3 3 3 .8 9 2 0 0 E -0 3 1 .2 I2 8 3 E -0 3 1.23446E -0S 0 .0 2 3 2 0 2 .3 4 8 4 3
4 3 .092 19
3 9 .9 9 3 3 3 3 .3 0 3 0 0 E -0 3 1.2 1 0 0 0 E -0 3 1 .0 9 7 3 IE -0 3 0.02041 2 .3 3 3 1 7
48.98991
4 4 .9 8 8 3 3 4 .8 3 4 3 3 E -0 3 I.2 0 9 4 0 E -0 3 9 .7 7 I9 2 E -0 6 0 .0 1 8 2 7 2 .3 6 4 3 6
34 . 71401
3 0 .1 4 1 6 4 4 .4 7 3 5 0 E -0 3 1.2 0 9 2 4 E -0 3 8 .7 3 1 3 4 E -0 4 0 .0 1 6 4 6 2 .3 4 9 3 7
60 .7 4 4 0 2
3 3 .2 3 3 3 3 4 .1 6 3 6 6 E -0 3 1 .2 0 8 I3 E -0 3 7 .9 2 8 9 5 E -0 4 0 .0 1 5 0 0 2 .3 7 4 1 4
66 .664 24
6 0 .3 2 0 0 0 3 .9 0 6 1 4E -0 3 I.2 0 4 2 5 E -0 3 7 .2 4 3 7 0 E -0 6 0 .0 1 3 7 8 2 .5 7 8 3 2
72 .536 57
6 4 .9 9 8 3 3 3 .7 0 0 4 6 E -0 3 1 .20424 E -03 6 .4 9 2 7 8 E -0 6 0 .0 1 2 8 0 2 .3 7 9 7 9
78 .106 87
70 .000 00 3 .3 1 30 0E -03 1.2 0 3 4 6 E -0 3 4 .1 9 1 7 8 E -0 4 0.01191 2.38241
83 .9 4 6 7 2
7 3 .2 3 3 3 3 3 .3 3 8 3 0 E -0 3 1 .2 0 I0 3 E -0 3 3 .7 3 0 4 1 E -0 4 0 .0 1 1 0 9 2 .3 834 0
90 .1 3 3 9 3
80 .400 00 3 .1 8 8 0 0 E -0 3 1 .1 980 2E -03 3 .3 3 3 0 4 E -0 6 0 .0 1 0 3 8 2 .3 8 4 6 3
96 .2 3 3 1 7
90 .8 8 3 3 3 2 .9 3 0 70E -03 1 .1 906 2E -03 4 .6 6 3 0 7 E -0 4 9 .1 9 8 2 4 E -0 3 2 .3 8 5 6 7
108.71633
99 .9 1 6 6 6 2 . 76283E -03 1.1 8 8 1 2 E -0 3 4 .2 2 1 7 1 E -0 4 8 .4 1 0 0 7 E -0 3 2 .3 9 2 3 7
118.90304
11 0 .3 4 6 6 6 2 . 39250E -0 3 1 .1 838 2E -03 3 .7 7 6 6 0 E -0 4 7 .4 1 8 7 9 E -0 3 2 .3 9 3 2 3
131.23443
1 2 0.73 333 2 .4 3 3 0 0 E -0 3 1 .I7 7 2 4 E -0 3 3 .4 2 0 2 6 E -0 6 4 .9 8 5 3 0 E -0 3 2 .5 9 7 0 8
14 3.13 763
1 3 0 .1 4 6 6 6 2 .3 3 4 8 3 E -0 3 1.1 7 3 3 2 E -0 3 3 .I1 3 4 0 E -0 6 4 .4 3 9 7 9 E -0 3 2 .3 8 9 1 9
135.28439
14 0 .4 6 6 6 4 2 .2 3 1 0 0 E -0 3 1.1 6 3 3 5 E -0 3 2 .8 5 6 4 0 E -0 4 3 .9 8 2 9 2 E -0 3 2 .3 9 2 3 2
167.14242
161.33 333 2 .0 3 6 0 0 E -0 3 1 .1 308 4E -03 2 .4 2 6 6 7 E -0 6 3 .2 I8 9 7 E -0 3 2 .3 9 6 3 8
191.60833
18 0.0 1 6 6 6 1 . 94566E -0 3 1.1 3 9 8 2 E -0 3 2 .1 6 0 4 2 E -0 6 4 .7 4 3 6 3 E -0 3 2 .6 1 3 8 4
21 0 .7 1 8 9 8
19 9.9 3 3 3 3 1 .8 3 1 0 0 E -0 3 1.1 2 6 4 3 E -0 3 1 .88 884 E -06 4 .2 4 2 8 6 E -0 3 2 .6 1 0 7 9
23 4 .3 8 4 0 3
2 1 9 .9 6 6 6 4 1 .7 2 4 7 6 E -0 3 1 .1 103 9E -03 1 .44 708 E -06 3 .8 3 3 0 7 E -0 3 2 .3 9 6 7 3
26 0.88 712
2 3 9 .9 3 0 0 0 1 .6 4 1 90 E -03 1 .09449 E -03 1 .46 736 E -06 3 .3 I3 9 4 E -0 3 2 .3 9 6 7 9
28 4 .3 8 0 7 2
2 3 9 .9 3 3 3 3 I.3 7 0 1 3 E -0 3 1 .07843 E -03 1 .3 1 7 4 1 E -0 4 3 .2 4 7 3 6 E -0 3 2.3 982 1
30 7.94 227
2 7 9 .9 0 0 0 0 1 .3 0 9 6 1 E -0 3 1 .06427 E -03 1 .1 9 3 9 1 E -0 6 3 .0 2 7 4 3 E -0 3 2 .4 0 3 2 7
3 3 0.31 020
2 9 9 .8 8 3 3 3 I.4 S 3 8 6 E -0 3 1 .04 671 E -03 1 .0 9 1 5 3 E -0 4 2 .8 4 3 4 4 E -0 3 2 .4 1 2 3 5
33 1 .4 3 6 8 3
M a t* o f tam p! • ( g r a n t ) •* 0.0 373 0
M o lt c u la r W tig h t ■ 1777.73000
D la n a g n ttle e o r r t c t I o n /T IP (* E - 6 ) “ -9 0 3 .0 0 0 0 0
Table 5-4. Variable temperature magnetic su sceptibility data for
Fe(TPP)(CuIm)2‘ 2toluene in 10KG magnetic fie ld . TEMP=temperature, K;
MAGSN=magnetization of sample and bucket; CORR=magnetization of buc
ket; CHIG=gram susceptibility; CHIM=molar su scep tibility; MUEFF=eff-
ective magnetic moment; and l/CHIM*reciprocal molar su scep tib ility.
138
are three S=l/2 centers. The room temperature magnetic moment of
3.48jLtg is s lig h tly higher than that expected for three independent
centers. (Assuming /xqu=1 . 77/zg and /zpe=2.10, the theoretical value is
3.19^0.) Extrapolation of the high temperature reciprocal molar
susceptibility vs. temperature plot (Figure 5-7) gives a small positive
intercept (5=1.85°) indicative of ferromagnetic coupling. This is also
displayed in the Meff vs- T P^ot (Figure 5-7) which shows a d e fin ite
increase at low temperature to /xeff=3.8/ig then a sharp decrease which
is undoubtedly caused by zero fie ld s p littin g of the iron and/or by a
small an ti ferromagnetic coupling between the copper centers.
Calculating the best theoretical f i t to this curve gives g=2.31, Jqu_
QU=-0.35cm'l and Jpe_cu=10cm~l. The small anti ferromagnetic in te r
action between the copper atoms is consistent with that found in the
ferrous bis-imidazolate complex in which J=-0.74cm_1. In the both
complexes, this interaction could be either in tra - or inter-molecular,
and support for the la tte r comes from the x-ray crystal structure of
the fe rric complex presented below. Comparison of the observed and
calculated values using these parameters (Figure 5-7) shows that only a
q u alitative f i t has been achieved, but the trends found in both are
sim ilar. Also i t has been shown that the theoretical susceptibility
data in ferromagnetically coupled systems is re la tiv e ly insensitive to
changes in J, so that the coupling constant of 10cm"! can only be used
as a rough estim ate.37 Table 5-6 gives the variable temperature
magnetic data. The Mossbauer parameters of 6=0.23mm/s and AEq=2.07mm/s
are consistent with low spin i r o n ( I I I ) .
Magnetic studies have revealed that the observation of a n tife r
romagnetic coupling is much more common than that of ferromagnetic
coupling. One estimate is less than 5% for the l a t t e r . 38 There have
been other trinuclear complexes containing three S=l/2 centers which
exhibit ferromagnetic coupling,39’ 40 but both are C u (II) trimers and
neither contain imidazolate bridges. This ir o n ( III) bis-copper(II)
complex is the f ir s t imidazolate bridged complex to exhibit
ferromagnetic coupling. The explanation for ferromagnetic coupling
undoubtedly lie s in the fact that the magnetic orbital of low spin
ir o n ( III) is the d y Z orbital which is of 7 r symmetry and therefore can
only overlap with the 7 r system of the imidazolate bridge. The copper
atom on the other hand, whose magnetic orbital is its d x 2 _ y 2 , can only
overlap with the a orbitals of the bridging imidazolate. I t is this
orthogonality of magnetic orbitals which prevents the unpaired
electrons from pairing and therefore favoring the S=l, or fe rro
magnetic, ground state.
X-ray quality crystals of this trinu clear imidazolate bridged
complex were grown by toluene diffusion into a concentrated DM F
solution. The x-ray structure was solved by Prof. W . R. Scheidt and
co-workers.41 This structure shown in Figure 5-8 confirms the
existence of the bis-copper imidazolate bridges on either side of
Fe(TPP). Another view of the structure (Figure 5-9) also shows the
short distance between the copper centers of adjacent molecules which
suggests that the small anti ferromagnetic coupling that exists between
the copper atoms could be either in te r- or intra-molecular.
2.50
5 0 0 -
-2 .2 5
4 0 0 -
^ 3 0 0 -V *##
x
- 2.00
2 00 -
-1 .7 5
100
1.50
0 25 50 75 100 125 150 175 200 225 250 275 300
Temperature, K
Figure 5-6. Plots of reciprocal molar susceptibility (triangles) and effective magnetic moment
(circles) vs. temperature for [Fe(TPP)(NiIm)2](B]iCH12)'5THF. For 1/ xm vs. T, solid line is
linear least-squares f i t with slope = 1.816, x-intercept = -0.10, and coefficient of correlation
- 0.99996.
TEMP PWGSN. CORR. CM1G CHIM HUEFF 1/CMIM
141
2 .4 600 0 0 .0 2 8 8 4 I.2 4 0 0 3 E -0 3 9 .9 2 8 0 3 E -0 5 0 .2 0 7 9 3 2 .0 2 2 7 0 4 .8 0 8 6 9
4 .3 1 0 0 0 0 .0 1 6 7 9 1 .2 3 4 1 6 E -0 3 3 .3 9 5 6 2 E -0 S 0 .1 1 7 3 2 2 .0 1 2 6 9 8 .3 0 9 0 0
6 .0 0 0 0 0 0 .0 1 2 7 0 I.2 1 9 5 3 E -0 3 4 .1 2 9 6 6 E -0 5 0 .0 8 6 9 2 2 .0 4 2 3 0 1 1 .304 34
7 .0 000 0 0 .0 1 1 0 0 1 .2 0 6 9 3 E -0 3 3 .3 2 2 6 8 E -0 5 0 .0 7 4 2 3 2 .0 3 8 8 3 1 3 .4 6 7 6 2
8 .0 0 0 0 0 9 .8 2 3 0 0 E -0 3 1 .2 0 4 3 9 E -0 3 3 .1 0 0 1 4 E -0 5 0 .0 6 3 4 3 2 .0 4 6 0 6 1 3 .2 8 3 0 2
10.00000 8 .1 3 2 6 6 E -0 3 1 .2 0 3 6 2 E -0 3 2 .4 9 2 4 3 E -0 3 0 .0 3 2 7 4 2 .0 339 0
18.93831
12.00000 6 .9 9 4 5 0 E -0 3 1 .2 0 1 1 3 E -0 3 2 .0 8 3 9 4 E -0 3 0 .0 4 4 2 2 2 .0 6 0 0 3
2 2 .614 17
1 4 .996 66 5 .8 4 0 8 3 E -0 3 I.2 0 0 6 3 E -0 3 1 .6 6 9 1 3 E -0 5 0 .0 3 3 3 6 2.06321
2 8 .1 2 0 3 9
2 0 .000 00 4 .6 6 0 8 3 E -0 3 I.1 9 9 I3 E - 0 3 I.2 4 5 2 0 E -0 S 0 .0 267 1 2 .0 6 7 0 4
3 7 .433 94
2 3 .000 00 3.9 6 S 1 0 E -0 3 I.1 9 7 I9 E - 0 3 9 .9 5 6 4 7 E -0 6 0 .0 2 1 3 0 2 .0 7 3 4 7
4 6 .3 0 3 0 3
3 0 .0 0 1 6 6 3 .3 0 2 3 3 E -0 3 I.1 9 3 4 7 E -0 3 8 .2 9 8 0 2 E -0 6 0 .0 1 8 0 4 2 .0 8 0 3 8
3 3 .4 2 8 6 3
3 5 .000 00 3 .1 7 3 3 0 E -0 3 1 .1 9 4 3 9 E -0 3 7 .1 2 5 5 4 E -0 6 0 .0 1 5 5 9 2 .0 8 9 2 4
6 4 .1 2 8 1 2
3 9 .9 9 8 3 3 2 .9 2 3 3 3 E -0 3 1 .1 9 3 2 9 E -0 3 6 .2 3 0 3 2 E -0 6 0 .0 1 3 7 2 2 .0 9 3 3 3
7 2 .8 3 9 1 3
4 4 .9 9 3 0 0 2 .7 1 490E -03 1 .1 9 1 7 9 E -0 3 S .4 7 8 7 8 E -0 6 0 ,0 1 2 1 5 2 .0 9 1 3 2
8 2 .2 6 1 3 !
3 0 .0 1 3 3 3 2 . 57033E -03 1 .1 8 9 9 1 E -0 3 4.9 6S S 3 E -06 0 .0 1 1 0 8 2 .1 0 5 6 7
9 0 .2 1 1 8 7
3 3 .2 7 3 3 3 2 .4 3 4 0 0 E -0 3 1 .1 8 8 8 0 E -0 3 4 .4 7 9 1 2 E -0 6 0 .0 1 0 0 6 2.10981
9 9 .3 0 7 9 2
60 .3 6 0 0 0 2 .3 2 4 6 6 E -0 3 1 .I8 6 3 9 E -0 3 4 .0 9 4 4 8 E -0 6 9 .2 6 6 7 9 E -0 3 2 .1 1 3 0 4
107.91220
6 4 .9 9 8 3 3 2 .2 3 7 6 6 E -0 3 1 .1 8 6 1 5 E -0 3 3 .7 8 2 4 0 E -0 6 8 .6 1 3 3 6 E -0 3 2 .1 1 6 2 3
11 6.07 173
69 .983 00 2 .1 3 3 0 0 E -0 3 1 .1 8 4 3 3 E -0 3 3 .4 8 3 6 8 E -0 6 7 .9 9 1 8 0 E -0 3 2 .1 1 4 9 4
123.12817
73 .330 00 2 .0 7 3 3 0 E -0 3 1 .1 8 2 3 9 E -0 3 3 .2 0 3 4 1 E -0 6 7 .4 1 0 9 3 E -0 3 2 .1 1 3 2 8
134.93340
8 0 .4 0 0 0 0 2 .0 0 9 3 3 E -0 3 1 .1 8 I2 0 E -0 3 2 .9 7 8 8 4 E -0 6 6 .9 3 8 0 1 E -0 3 2 .1 1 2 1 3
144.13334
9 0 .0 0 0 0 0 1 .9 0 9 6 6 E -0 3 1 .1 7 6 4 9 E -0 3 2 .6 3 7 2 6 E -0 6 6 .2 2 3 0 0 E -0 3 2 .1 1 6 7 3
160.64248
9 9 .9 0 0 0 0 1 .8 0 9 9 1 E -0 3 1 .I7 1 9 0 E -0 3 2 .2 9 4 9 7 E -0 6 5 .5 1 0 3 0 E -0 3 2 .0 9 8 2 3
1 8 1.47 152
1 1 0.86 666 1 .7 3 1 1 0 E -0 3 1 .1 6 7 S 6 E -0 3 2 .0 2 7 1 0 E -0 6 4 .9 5 1 3 6 E -0 3 2 .0 9 5 2 8
201 .96439
120.20000 1 .6 6 6 3 6 E -0 3 I.1 6 I1 3 E - 0 3 1 .8 I7 2 8 E -0 6 4 .3 1 3 3 8 E -0 3 2 .0 8 2 9 6
221.36321
13 0.5 3 3 3 3 1 .6 1 496E -03 1 .1 S 3 18E -0 3 I.6 6 1 0 7 E -0 6 4 .1 8 7 3 1 E -0 3 2 .0 9 0 7 7
238.81670
1 4 0.13 333 1 .3 7 7 2 3 E -0 3 I.1 4 8 4 8 E -0 3 1 .3 4 2 3 0 E -0 6 3 .9 3 9 3 9 E -0 3 2 .1 0 1 1 8
23 3.84 600
161.53000 1 .4 8 4 3 8 E -0 3 1 .1 3 3 0 8 E -0 3 1 .2 6 4 3 5 E -0 6 3 .3 3 9 2 0 E -0 3 2 .0 8 3 2 9
29 7 .6 8 9 6 3
18 0.0 1 6 6 6 1 .4 3 4 9 3 E -0 3 1 .1 2 2 2 2 E -0 3 1 .1 2482E -06 3 .0 6 7 9 3 E -0 3 2 .1 0 1 6 4
32 5 .9 3 1 7 8
19 9.9 8 3 3 3 1 .3 7 8 6 6 E -0 3 1 .1 0 8 6 3 E -0 3 9 .7 1 2 3 6 E -0 7 2 .7 4 7 3 4 E -0 3 2 .0 9 6 2 0
363.98731
2 1 9.93 000 I .3 3 1 70E -03 1 .0 9 3 9 3 E -0 3 8 .3 3 2 6 0 E -0 7 2 .3 0 5 2 6 E -0 3 2 .0 9 9 2 6
39 9 .1 5 9 8 6
2 3 9 .8 8 3 3 3 I.2 8 9 8 6 E -0 3 1 .0 7 9 0 5 E -0 3 7 .3 8 2 8 8 E -0 7 2 .3 0 2 8 4 E -0 3 2 .1 0 1 8 9
4 3 4 .2 4 3 6 3
2 3 9 .8 8 3 3 3 I.2 4 8 3 8 E -0 3 1 .0 6 3 0 4 E -0 3 6 .6 6 6 3 4 E -0 7 2 .1 1 IS 6 E -0 3 2 .0 9 4 9 3
473.38161
27 9 .8 3 0 0 0 1 .2 1 40 0E -03 1 .0 4 7 5 9 E -0 3 5 .9 8 3 6 1 E -0 7 1 . 96943E -0 3 2 .0 9 9 4 8
3 0 7 .7 6 0 9 6
2 9 9 .7 6 6 6 6 I.1 8 1 3 6 E -0 3 1 .0 3 2 6 3 E -0 3 3 .3 4 8 9 2 E -0 7 1 .8 3 6 3 2 E -0 3 2 .0 983 1
3 4 4 .3 0 3 3 8
M as* oF ts m p lK g r u n t) “ 0 .0 2 7 8 0
M o lt c u ls r U s ig h t » 20 87 .3 9 0 0 0
01 unsgn* 11e c o r r s c 1 ie n /T IP <«E-6> * -7 2 0 .0 0 0 0 0
Table 5-5. Variable temperature magnetic su sceptibility data for
[Fe(TPP)(NiIm)?](BjjCH^) *5THF in 10KG magnetic fie ld . TEMP=temp-
erature, K; W\GSN=magnetization of sample and bucket; CORR=magne-
tiza tio n of bucket; CHIG=gram su sceptibility; CHIM=molar suscep
t i b i l i t y ; MUEFF=effective magnetic moment; and l/CHIM=reciprocal molar
susceptibility.
200 4.0
150 -3 .5
100 -3 .0
5 0 - -2 .5
2.0
0 25 50 75 100 125 150 175 200 225 250 275 300
Temperature, K
Figure 5-7. Plots of reciprocal molar susceptibility and effective magnetic moment vs. temp
erature for [Fe(TPP)(CuIm)2 ](BuCHi2 )-5THF. For 1/xm (triangles) vs. T, solid line is linear
least-squares f i t with slope = 0.67, x-intercept = 1.85, and coefficient of correlation =
0.99986. For nQf f (circles) vs. T, curve is theoretical f i t with g = 2.31, Jcu-Cu = -0*35,
and Jfe-Cu “ 10*lcm .
TEMP PMOSN. COMt. OHIO CH1H MUEPF 1/CHIM J 4 3
2 .0 2 0 0 0 0 .1 0 4 9 0 1.2 4 6 8 4 E -0 3 2 .7 7 2 8 6 E -0 4 0 .6 2 8 7 2 3 .1 8 7 0 2 I .3 7 0 3 2
4 .2 7 0 0 0 0 .0 6 6 2 3 I.2 3 4 2 0 E -0 3 1 .87 8 4 7 E -0 4 0 .3 7 3 0 3 3 .6 8 1 4 7 2 .3 3 1 4 3
3 .3 8 0 0 0 0 .0 3 3 7 8 1.2 2 6 2 7 E -0 3 I.3 7 6 6 7 E -0 4 0 .3 3 1 7 4 3 .7 7 8 0 8 3 .0 1 4 3 6
6 .0 0 0 0 0 0 .0 3 1 4 3 I.2 I7 S 3 E -0 3 I.4 3 1 7 4 E -0 4 0 .3 0 5 3 4 3 .8 2 7 0 4 3 .2 7 2 8 7
7 .0 0 0 0 0 0 .0 4 4 4 3 1.2 0 6 7 3 E -0 3 1 .2 4 7 2 2 E -0 4 0 .2 6 3 0 7 3 .8 3 7 6 4 3 .8 0 1 2 6
8 .0 0 0 0 0 0 .0 3 7 0 7 1 .2 0 4 3 7 E -0 3 1.0 7 4 7 5 E -0 4 0 .2 307 1 3 .8 4 2 0 8 4 .3 3 4 2 6
1 0 .0 0 0 0 0 0 .0 3 1 3 7 1 .20362E -03 8 .7 2 4 3 8 E -0 3 0 .1 8 4 0 3 3 .8 3 6 6 7 3.4 3 3 1 1
1 2 .0 0 0 0 0 0 .0 2 6 1 4 I.2 0 U 3 E -0 3 7 .2 0 7 7 6 E -0 3 0 .1 5 2 2 3 3 .8 2 2 3 3 6 .3 6 8 0 6
1 3 .0 0 0 0 0 0 .0 208 1 I.2 0 0 6 3 E -0 3 3.6 674 4E -Q 3 0 .1 1 7 7 3 3 .7 7 3 3 7 8 .3 3 6 7 8
2 0 .0 0 0 0 0 0 .0 1 3 3 5 1 .1 791 3E -03 4 .0 8 7 8 3 E -0 3 0 .0 8 6 8 6 3 .7 2 7 3 3 1 1 .3 1 1 8 8
2 3 .0 0 0 0 0 0.0 1 2 2 1 1 .1 771 7E -03 3.1 8 2 8 7 E -0 S 0 .0 6 7 8 4 3 .6 8 3 1 2 1 4 .7 3 8 7 3
3 0 .0 0 0 0 0 0 .0 1 0 1 8 I.1 7 3 4 7 E -0 3 2 .3 7 6 6 8 E -0 3 0 .0 3 3 3 3 3 .6 3 0 8 8 1 8 .0 0 0 4 2
3 3 .0 0 0 0 0 8 .7 8 7 3 0 E -0 3 I.1 7 4 3 7 E -0 3 2 .1 7 4 4 2 E -0 3 0.0 471 1 3 .6 316 7
2 1 .2 2 3 0 3
4 0 .0 0 0 0 0 7 .7 3 1 30E -03 I.1 7 3 2 7 E -0 3 1.887S 7E -0S 0 .0 4 0 7 2 3 .6 0 7 4 7
2 4 .3 3 4 2 3
4 4 .7 7 2 0 0 6 .7 2 4 7 0 E -0 3 1 .1 717 7E -03 I.6 3 6 7 0 E -0 S 0 .0 3 3 8 4 3 .3 7 1 4 5
27 .876 71
3 0 .1 7 3 0 0 6 .2 6 3 2 0 E -0 3 1 .1 878 3E -03 1 .4 6 6 8 6 E -0 3 0 .0 3 1 8 6 3 .3 7 6 2 8
31 .386 21
3 3 .2 3 2 0 0 3 .7 4 7 3 0 E -0 3 1 .I8 8 8 0 E -0 3 1 .3 1 7 3 4 E -0 3 0 .0 2 8 7 2 3 .3 6 3 0 2
3 4 .8 0 7 1 2
6 0 .3 3 3 0 0 5 .3 1 300E -03 1 .1 863 7E -03 1.1 7 2 6 5 E -0 S 0.02611 3 .3 4 7 3 6
3 8 .2 7 8 1 8
6 4 .7 8 7 0 0 4 .7 7 3 3 0 E -0 3 1 .I8 6 1 3 E -0 3 I.0 9 3 1 8 E -0 3 0 .0 2 4 0 6 3 .3 3 6 7 3
4 1 .3 3 0 7 4
7 0 .0 0 0 0 0 4 .6 3 6 8 0 E -0 3 I.I8 4 3 2 E -0 3 1 .0 0 3 3 4 E -0 3 0 .0 2 2 1 4 3.3 2 1 0 0
4 3 .1 3 6 7 8
7 3 .2 8 3 0 0 4 . 37600E -03 1 .1 6 2 4 IE -0 3 7 .2 3 0 0 1 E -0 6 0 .0 2 0 4 3 3 .3 0 7 4 4
4 8 .8 8 3 4 3
8 0 .4 0 0 0 0 4 . 1 3420E -03 1.1 8 1 2 0 E -0 3 8 .S 3 4 6 3 E -0 6 0 .0 1 8 7 7 3 .4 7 3 0 7
3 2 .6 3 7 7 7
7 0 .7 6 7 0 0 3 .7 3 8 0 0 E -0 3 1.1 7 6 0 3 E -0 3 7 .4 0 4 3 1 E -0 6 0 .0 1 6 6 2 3 .4 7 8 0 7
6 0 .1 4 0 2 7
7 7 .7 1 7 0 0 3 .4 8 6 3 0 E -0 3 1 .1 7 I8 7 E -0 3 6 .6 8 7 0 1 E -0 6 0 .0 1 3 1 2 3 .4 7 6 8 0
6 6 .1 0 3 4 8
1 1 0 .6 3 3 0 0 3 .2 3 0 2 0 E -0 3 1 .I6 7 6 7 E -0 3 3 .7 6 1 0 0 E -0 6 0 .0 1 3 6 0 3 .4 6 8 7 7
73 .3 2 3 7 1
1 2 0 .7 8 3 0 0 3 .0 1 370E -03 I.1 6 0 7 2 E -0 3 3 .3 6 1 17E -06 0 .0 1 2 3 4 3 .4 3 2 7 4
8 1 .0 1 8 8 3
1 3 0 .3 3 3 0 0 2 .8 3 0 7 0 E -0 3 1.1 5 3 3 0 E -0 3 4 .7 0 3 7 3 E -0 6 0 .0 1 1 3 8 3 .4 4 3 2 8
8 7 .8 1 3 8 7
1 4 0 .6 6 7 0 0 2 . 70850E -03 1 .1 4 8 I7 E -0 3 4 .3 0 7 3 6 E -0 6 0 .0 1 0 3 3 3 .4 4 6 2 2
7 4 .7 2 3 0 2
1 6 1 .3 3 3 0 0 2 .4 3 7 3 0 E -0 3 1.1 3 3 1 0 E -0 3 3 .8 3 2 7 4 E -0 6 7 .1 3 7 7 3 E -0 3 3 .4 3 3 8 3
1 0 7 .4 3 3 6 2
1 8 0 .0 1 7 0 0 2 .3 1 4 0 0 E -0 3 1.1 2 2 2 2 E -0 3 3 .4 4 4 4 2 E -0 6 8 .3 2 3 1 7 E -0 3 3 .4 6 1 6 3
1 2 0 .1 4 6 1 6
1 7 7 .7 8 3 0 0 2 . 16380E -03 1 .I0 8 6 3 E -0 3 3 .0 3 3 3 2 E -0 6 7 .3 0 7 2 3 E -0 3 3 .4 6 3 1 0
13 3.20 481
2 1 7 .7 3 0 0 0 2 .0 3 7 2 0 E -0 3 1 .07 373 E -03 2 .7 2 6 I7 E -0 6 6 .8 I7 0 1 E -0 3 3 .4 6 2 8 8
1 4 6 .6 7 1 7 6
2 3 7 .7 0 0 0 0 1 .7 3 0 7 0 E -0 3 1 .0 7 7 0 4 E -0 3 2 .4 6 1 4 3 E -0 6 6 .2 6 1 8 0 E -0 3 3 .4 6 6 1 2
1 3 7 .6 7 8 3 3
2 3 7 .8 3 0 0 0 1.838S 0E -A 3 I.0 6 3 0 7 E -0 3 2 .2 4 1 10E -06 3 .7 7 7 7 6 E -0 3 3 .4 7 1 7 2
17 2 .4 2 0 8 4
2 7 7 .8 3 0 0 0 1 .7 3 7 6 0 E -0 3 1 .04 737 E -03 2 .0 3 2 0 2 E -0 6 3 .4 0 3 2 3 E -0 3 3.4 773 1
1 8 3 .0 7 4 2 7
2 7 7 .7 8 0 0 0 1 .6 8 4 7 0 E -0 3 1 .0 3 2 8 IE -0 3 I.8 8 4 6 2 E -0 6 3 .0 3 2 1 7 E -0 3 3 .4 8 0 3 3
1 7 7 .7 3 3 7 0
H m o4 4klnpI• (gr«T>»> ■ 0.03460
Mol»cv1»r Wolght - 2077.07000
D l* n « g n * tlc c o r r » e tl o n /T IP <»t-6> “ -1100.00000
Table 5-6. Variable temperature magnetic su sceptibility data for
[Fe(TPP) (Culm)?] (Bi iCH^) '5THF in 10KG magnetic fie ld . TEMP=temp-
erature, K; MAGSN=magnetization of sample and bucket; CORR=magne-
tiza tio n of bucket; CHIG=gram su sceptibility; CHIM=molar suscep
t i b i l i t y ; MUEFF=effective magnetic moment; and l/CHIM=reciprocal molar
su sceptibility.
144
Figure 5-8. A view of the [Fe(TPP)(Culm)?](Bi j CHu ) - 4DMF molecule.
Only one solvent molecule is shown, and tne carborane anion is deleted
fo r c la rity .
Figure 5-9. Alternate view of two [Fe(TPP)(Culm)] (BuCHj?)-4DMF molecules showing the
interaction between adjacent copper centers. Only one solvent molecule is shown, and the
carborane anion is deleted for c la rity .
145
146
Manqanese(II) Metal Imidazolate Complexes
Manganese (II) porphyrins have been shown to coordinate only one
axial ligand even in the presence of excess ligands such as 1-methyl -
imidazole, 2-methyl imidazole, and pyrid ine.22 This is apparently due
to the in a b ility of these ligands to cause a change of the spin state
of the M n(II) from high spin, S=5/2, to low spin, S=l/2. Because of
this the metal lie s outside the plane of the porphyrin (0.52A in
Mn(TPP)(l-Melm)23) and hence cannot coordinate a sixth ligand. The
preference for 5-coordination of M n(II) tetraphenyl porphyrin was used
to our advantage in forming binuclear imidazolate bridged species
rather than the trinu clear species already presented in the ferrous and
fe rric porphyrins. Also, M n(II) having five unpaired electrons is
isoelectronic to high spin F e ( III) and therefore a good spin model for
the F e ( III) center in cytochrome c oxidase.
Mn(TPP)(NiIm) exhibits a re la tiv e ly constant magnetic moment
between 5 .7 5 -5 .8 7 ^ at high temperatures and shows a slight decrease
below 30K. The room temperature magnetic moment of 5.87/zg is typical
of high spin M n(II) compounds. Table 5-7 gives the variable tem
perature data, and Figure 5-10 shows the plots of reciprocal molar
susceptibility and magnetic moment vs. temperature for 6-300K. The g
value calculated from the l/x\\ vs. T plot is 1.98, s lig h tly lower than
the free electron g value of 2.00.
The copper analogue, Mn(TPP)(Culm), contains two antiferromag-
n e tica lly coupled metal centers, M n (II), S=5/2, and C u (II), S=l/2.
This is demonstrated by a lower room temperature magnetic moment,
5 .84/xg, than theoretically expected, 6.13/ig, assuming /i^n=5.87 as in
147
the nickel analogue and /liqu=1.77 as in the Culm complex. Also, the
magnetic moment shows a large decrease at low temperatures to 4.33 1 1% .
Figure 5-11 plots the reciprocal molar susceptibility and magnetic
moment vs. temperature for 2.5 to 300K. The best theoretical f i t for
the magnetic moment data gives g=1.90, D=1.16cm~l, and J=-6.01cm_1.
This g value is s lig h tly lower than expected, but setting g equal to
2.00 and varying only the zero fie ld s p littin g and J results in a very
poor f i t . The g value calculated from the 1/xm data is even lower at
1.71. The negative intercept of this plot (0=111.73°) is consistent
with anti ferromagnetic coupling. Table 5-8 gives the variable temper
ature data.
In order to compare the nickel and copper imidazolate complexes of
Mn(TPP) to a simple imidazolate complex, Mn(TPP)(l-Melm) was prepared.
I t had been synthesized prior to this work,22’ 23 but variable temper
ature magnetic measurements were not conducted at that time. The
magnetic moment remains fa ir ly constant at -5.8/Ltg from 6 to 300K
(Figure 5-12), and there is a sharp decrease at lower temperatures.
The g value calculated from the 1/xm v s . T plot (Figure 5-12) is 1.99
in excellent agreement with that of Mn(TPP)(NiIm). Table 5-9 gives the
variable temperature magnetic data.
Capped Porphyrin Metal Imidazolate Complexes
The Baldwin capped porphyrin27 consists of a tetraphenyl porphyrin
base connected via ester and ether linkages to a tetrasubstituted
phenyl ring (Figure 5-13). The bulky appendage was designed to block
70 6.0
6 0 - ........
-5 .5
5 0 -
X
5.0
3 0 -
-4 .5
4.0
0 25 50 75 100 125 150 175 200 225 250 275 300
Temperature, K
Figure 5-10. Plots of reciprocal molar susceptibility (triangles) and effective magnetic moment
(circles) vs. temperature for Mn(TPP)(NiIm)*3toluene. For 1 / xm v s . T, solid line is linear
least-squares f i t with slope - 0.23, x-intercept - -2.03, and coefficient of correlation - £
0.99990. 00
TEMP MA6SN. CORR. C H I6 CHIM MUEFF 1 /C H IM
149
6.00000 0.07733 1.39106E-03 4.63042E-04 0.65009 5.58525 1.53823
7.00000 0.06695 1 .39066E-03 3.99752E-04 0.56137 5.60604 1.78132
8.00000 0.05923 1.38781E-03 3.52696E-04 0.49541 5.63003 2.01849
10.00000 0.04807 1.38164E-03 2.84685E-04 0.40008 5.65660 2.49946
15.00166 0.03284 1.37415E-03 1.91864E-04 0.26997 5.69131 3.70402
20.00000 0.02496 1.36159E-03 1.43S92E-04 0.20273 5.69450 4.93260
25.00000 0.02031 1 . 36244E-03 1.15533E-04 0.16298 5.70845 6.13567
30.00000 0.01727 1 .36059E-03 9.70085E-05 0.13701 5.73352 7.29853
34.99330 0.01505 1.35360E-03 8.35146E-05 0.11809 5.74903 8.46747
39.99666 0.01327 1.35430E-03 7.26566E-05 0.10287 5.73660 9.72015
44.99333 0.01196 1.3S174C-03 6.46844E-05 0.09170 5.74444 10.90463
50.01333 0.01092 1.34736E-03 5.83697E-05 0.08285 5.75672 12.06963
55.26833 0.01003 1.34845E-03 5.29362E-05 0.07523 5.76675 13.29145
60.35000 9 . 29430E-03 1.34638E-03 4.84628E-05 0.06896 5.76945
14.49992
64.99833 8.72933E-03 1.34198E-03 4.50447E-05 0.06417 5.77579
15.58247
69.98333 8.18300E-03 1.33902E-03 4.17315E-05 0.05953 5.77225
16.79815
75.30000 7.67866E-03 1.33931E-03 3.86545E-05 0.05521 5.76652
18.11028
80.40000 7 . 26233E-03 I.33449E-03 3.61453E-05 0.05169 5.76570
19.34237
90.00000 6.62533E-03 1.32882E-03 3.22957E-05 0.04630 5.77310
21.59642
99.91666 6.06933E-03 1.32680E-03 2.89178E-05 0.04156 5.76345
24.05641
110.70000 5 .6 1 066E-03 1.31884E-03 2.61696E-05 0.03771 5.77856
26.51342
120.63333 5.22166E-03 1.31241E-03 2.38368E-05 0.03444 5.76484
29.03023
130.36666 4.91250E-03 1.3O147E-03 2.20184E-05 0.03189 5.76691
31.35000
140.73333 4 . 64450E-03 1.29986E-03 2.03940E-05 0.02962 5.77401
33.75982
160.05000 4.25383E-03 1.28513E-03 1.81017E-05 0.02640 5.81398
37.86757
180.03333 3.89666E-03 1.2714CE-03 1.60076E-05 0.02347 5.81345
42.60329
199.96666 3.61583E-03 1.25626E-03 1.43876E-05 0.02120 5.82293
47.16640
219.93333 3.38266E-03 1.23882E-03 1.30721E-05 0.01935 5.83513
51.65916
239.90000 3.181OOE-03 1.22I52E-03 1.19480E-05 0.01778 5.84095
56.23694
259.86666 3.01400E-03 1.20566E-03 1.10264E-05 0.01649 5.85418
60.64248
279.83000 2 . 86366E-03 1.18761E-03 1.02198E-05 0.01535 5.86291
65.10668
299.76666 2.73216E-03 1.17055E-03 9.52200E-06 0.01438 5.87177
69.53485
Hass oi samp Ie(grams! * 0.01640
M olecular Weight = 1401 .73000
Diamagnetic c o r re c tio n /T IP <»E-6> « -1034.00000
Table 5-7. Variable temperature magnetic susceptibility data for
Mn(TPP)(NiIm)*3toluene in 10KG magnetic fie ld . TEMP=temperature, K;
MAGSN=magnetization of sample and bucket; CORR=magnetization of buc
ket; CHIG=gram susceptibility; CHIM=molar susceptibility; MUEFF=eff-
ective magnetic moment; and l/CHIM=reciprocal molar susceptibility.
100
-5 .5 75
^—
4.5
4.0
250 300 200 150 50 100 0
Temperature.K
Figure 5-11. Plots of reciprocal molar susceptibility and effective magnetic moment vs.
temperature for Mn(TPP)(Culm)‘toluene. For 1/xm (triangles) vs. T, solid line is linear least-
squares f i t for data above 25K, with slope = 0.23, x-intercept = -11.7, and coefficient of
correlation = 0.99992. For Heff (circles) vs. T, curve is theoretical f i t with g = 1.90, D =
1.16, and J = -6.01cm-1.
i n
Q
TEMP M ABSN. CORR. C H IB CHIM HUE PR 1 /C H tM
2.32000 0.23970 I.2 S 2 90E -03 7.59040E -04 0.92941 4.3 2 7 9 7 1.07394
3.20000 0.18937 1.25121E-Q3 3.99104E -04 0.73319 4 .3 3 1 7 0 1.34388
4.13000 0.1 321 8 1 .24807E-03 4.80474E -04 0.38844 4.4 084 7 1.49938
4.40000 0.13440 I.2 4 4 1 7 E -0 3 4.30424E -04 0.32703 4.4 0 3 2 8 1.89742
3.00000 0.1 279 3 I.2 4 4 3 8 E -0 3 4.03521E -04 0.49414 4.44320 2.02349
3.30000 0.1 179 7 1.24192E -03 3.71745E -04 0.45330 4.47320 2.19431
5.99444 0.10393 1.23923E -03 3.33410E -04 0.40843 4.4 239 3 2.44824
4.99833 0 .0 919 7 1.23309E -03 2.88971E -04 0.33413 4.4 3 2 0 4 2.82377
8.00000 0.08131 1.22880E -03 2 . SS472E-04 0.31343 4 .4 781 3 3.19044
10.00000 0.06692 I.2 2 3 9 1 E -0 3 2 .0 9216E-04 0.23663 4.5 305 8 3.89627
12.00500 0.05727 1 .22424E-03 1 .78489E-04 0.21909 4.5 864 8 4.56415
14,99500 0.04771 1 .22386E-03 1.48045E-04 0.18188 4.67039 3.49790
19.99800 0.0 385 6 1 .2 1 987E-03 1 .18917E-04 0 . 14628 4.8 369 8 6.83391
25.00000 0.03244 1 .2 1 723E-03 9 . 94355E-05 0.12247 4.94847 8.16499
30.00000 0.0 284 2 1.2 1610E-03 8.66365E -05 0.10683 5.0 627 6 9.36062
35.00000 0.02545 1.21282E-03 7.71884E -05 0.09328 5.1 643 9 10.49312
39.99670 0.02307 1 .20999E-03 6 .9 6 1 78E-03 0.08602 5.2 458 2 11 .62397
44.99200 0.0 210 3 1 .20939E-03 6 .3 1 866E-Q3 0.07816 5.30350 12. 79287
SO.19800 0.01933 1 .20924E-03 5 . 77094E-05 0.07147 5 .3 3 6 6 8 13. 991 U
55.26300 0 .0 i 796 1.2 0814E-03 5 . 33498E-05 0.06614 5.4 0 6 8 7 15. 11820
60.34800 0.01676 1 .20424E-03 4.93406E -03 0.06148 5.44767 16. 26293
63.00500 0.0 157 8 1 .20424E-03 4 .6 4 1 95E-05 0.05767 5.4 7 5 7 7 17. 33839
70.00000 0.01465 1 .20346E-03 4 . 34603E-05 0.05405 5 .5 0 ! 20 18.49872
73.30000 0.01397 1.20101E-03 4 . 06635E-03 0.05064 5 .5 2 2 4 3 19. 74650
80.40000 0.0 131 8 1 . 19802E-03 3 .8 1 5 9 )E-OS 0.04737 5.33110 21 . 01 794
90.00000 0.01204 1 .19108E-03 3 .43306E-05 0.04316 3.3 741 8 23. 16535
99.91666 0.01105 1 .18812E-03 3 .1 4072E-05 0.03932 3.60579 23. 42839
110.40000 0.01014 1 .1 8370E-03 2.85232E -03 0.03380 3 .4 2 7 3 4 27.93231
120.48333 9.3 773 3E -03 1.17724E -03 2.41148E -03 0.03283 3.43141
30.43478
130.28333 8.78914E -03 I.1 7 3 4 4 E -0 3 2.42338E -03 0.0 305 8 3.4 449 3
32.49847
140.44444 8.2 403 0E -03 1.14341E -03 2.23938E -0S 0 .0 2 8 3 3 3.44791
33.01893
141.30000 7.32414E -03 1.13087E -03 1.94401E -03 0.0 249 4 3.4 787 9
40.03133
180.01444 4.7 794 4E -03 1.13982E -03 1.79412E -03 0.0 228 9 3 .7 407 8
43.48443
200.01444 4 .2 I7 3 0 E -0 3 1.12439E -03 1 .4 2 I3 7 E -0 3 0.0 207 3 3.7 420 3
48.18032
219.94444 S.7S400E-03 1.11039E -03 1 .47949E-03 0.01902 3.7 844 3
32.37282
239.91444 3 .3 3 3 I4 E -0 3 1.094S2E-03 1.33423E -03 0.01731 3.79714
37.09409
239.88333 3.0 181 4E -03 1.07849E-03 1.2S440E-03 0.01427 3,8 134 2
41.43320
279.84444 4.71483E -03 1.04430E -03 1.14322E -03 0.0 131 3 3.8 242 7
43.98211
299.78333 4.4 393 0E -03 I.0 4 4 8 IE -0 3 I.0 8 4 8 4 E -0 3 0.01422 3.83934
70.31334
M a tt o i tamp I • (gram t> • 0.03140
M o ltc u la r W .lQ ht * 1222.24000
D laraasnattc c o r r a c ( io n /T IP <»E-4) ■ -9 38.0 000 0
Table 5-8. Variable temperature magnetic susceptibility data for
Mn(TPP)(Culm)-toluene in 10K6 magnetic fie ld . TEMP=temperature, K;
MAGSN=magnetization of sample and bucket; CORR=magnetization of buc
ket; CHIG=gram susceptibility; CHIM=molar susceptibility; MUEFF=eff-
ective magnetic moment; and l/CHIM*reciprocal molar susceptibility.
6 . 0
-5 .5
50
4 0 -
-5 .0
\ 3 0 -
-4.5
4.0
0 25 50 75 100 125 150 175 200 225 250 275 300
Temperature, K
Figure 5-12. Plots of reciprocal molar susceptibility (triangles) and effective magnetic moment
(circles) vs. temperature for Mn(TPP)(l-MeIm). For 1 / xm v s . T, solid line is linear least-
squares f i t with slope = 0.23, x-intercept - -1.52, and coefficient of correlation - 0.99992.
TEMP FttG S N , CORR. C H IG CHIM MUEFF l/ C H IM 153
2.29000 0.44624 1.42934E -03 1 .8 0 IS 9 E -0 3 1.48140 S .20909 0.47494
2.90000 0.39434 I . 4233PE-03 1 .3 3 I3 3 E -0 3 1.23943 3.40303 0.7 938 8
4.00000 0.31084 1.41S 44E -03 I.1 9 9 3 1 E -0 3 0.98434 5.41788 1.01341
3.09000 0.23320 1.41418E -03 9.8 344 5E -04 0.80931 3.73980 1.23341
3.50000 0.23890 1.41134E -03 9.20498E -04 0.73739 3.77193 1.32031
3.99833 0.2 111 9 1.40102E -03 8 .1 313 5E -04 0.44914 5.44572 1.49443
4.99833 0.1 821 9 1 .39400E-03 7 .0 0 7 3 IE -0 4 0.37477 3.48172 1.73377
8.00000 0 .1 404 8 I.3 9 4 7 9 E -0 3 4.1 440 9E -04 0.50741 3.49891 1.94999
9.99833 0.1 291 4 1.39203E -03 4.93147E -04 0.40778 5.71027 2.43229
12.00000 0.10817 1 .3 8819E-Q3 4 .1 388 26-04 0.34098 5.72034 2, 93244
14.99833 0.0 847 8 1 .3 875 1E-03 3 .3 0 9 7 8 6 -0 4 0.27284 5.72082 3, 44509
20.00000 0.04508 1 .37590E-03 2 .4 491 56-04 0.20374 5.70877 4 . 90799
24.99444 0.05237 1 .37278E-03 1 .97443E-04 0.14324 5.71308 4. 12491
2 9 .9 9 6 6 6 0.04402 1 .34720E-03 1 .453206-04 0.13448 5.72430 7. 31413
34.99833 0.03809 1 .34453E -03 1 .42339E-04 0.11779 5.74202 8. 48938
39.99500 0.03341 1.3 425 06-03 1 .249906-04 0 .10353 5.75472 9.43841
44.99833 0.0 3 0 0 7 1,3 434 46-03 1 .1 I244E -04 0.09223 3.741 93 10 .83974
S O .12000 0.0 272 3 1.3 409 46-03 1 .00247E-04 0.08321 5.77541 12 .01720
55.18833 0.02490 I .35 743 6-0 3 9 .1 2 5 0 2 6 -0 5 0.07580 3.78421 13 .19222
40.25333 0.02294 1.3 541 36-03 8.3438 3E -05 0.04954 5.78970 14 .37543
44.97333 0.02135 1.3554 46-03 7.74982E -05 0.04449 3.78924 15 .50414
49.95000 0.01983 1.3515 96-03 7 .1 4 9 9 2 6 -0 5 0.05973 5.78047 14 .74131
75.21444 0.01857 1.3 443 46-03 4 .4 7 5 8 3 6 -0 5 0.03547 3.78498 17 .94233
80.28333 0.01744 1.3 482 76-03 4 .2 4 4 8 5 6 -0 5 0.05212 3.78537 19 .18320
90,73333 0,01542 1.3425 86-03 3 .5 3 3 8 8 6 -0 5 0,04428 3.79540 21 .40318
99.90000 0.0 142 4 1.3 349 46-03 5 .0 0 9 7 0 6 -0 5 0.04197 3.79117 23 .82248
110.40000 0.01301 1.32885E -03 4.3 2 7 5 7 E -0 3 0.03801 3.7 934 2 24 .3 0 4 1 3
120.70000 0.0 120 3 1.32458E -03 4 .1 493 8E -03 0.03490 3.80449 28 .448 80
130.84444 0.0 111 9 1.31832E -03 3.8242 3E -05 0.03224 5.80970 31 .008 39
140.78333 0.01043 1.31025E -03 3 .3 347 8E -03 0.02985 3.7 974 8 33 .4 9 4 3 4
141.48333 9 .2 5 4 1 4E -03 1 .29482E -03 3 .0 8 S 0 IE -0 3 0.02415 3.81573
38.23072
179.98333 8 . 44823E -03 I.2 8 1 9 7 E -0 3 2.78537E -05 0.02349 3.84004
42.20434
199.91444 7 .7 278 3E -03 1.24449E -03 2 .5 0 4 3 IE -0 5 0.02138 5.84720
44.74400
219.84444 7 .1 180 8E -03 1.23007E -03 2.27442E -03 0.01949 3.83482
31.29483
239.81444 4.3 9 3 3 3 E -0 3 1.233S 3E -03 2.07821E -03 0.01788 3.83429
59.9231A
239.81444 4 .1 730 8E -03 I.2 1 4 2 4 E -0 3 1.92202E -03 0.0 145 9 3.87272
40.24831
279.83333 3.8 0 4 0 0 E -0 3 I.1 9 3 4 4 E -0 3 I.7 8 4 9 3 E -0 3 0.01348 3.8 873 7
44.34732
299.49000 5 .4 3 3 I4 E -0 3 I.1 8 4 0 8 E -0 3 I.4 S 3 9 0 E -0 3 0.01439 3.8 734 5
49.47279
' H«m o l ..m p 1 .(g r*m « > * 0.02380
M o l.c u t « r W. ig h t - 821.94000
D iu n .g n .tic c o r r .c 1 1 o n /T IP <»E-4> “ -800.0 000 0
Table 5-9. Variable temperature magnetic susceptibility data for
Mn(TPP)(l-Melm) in 10KG magnetic fie ld . TEMP=temperature, K;
MAGSN=magnetization of sample and bucket; C0RR=magnetization of buc
ket; CHIG=gram susceptibility; CHIM-molar susceptibility; MUEFF=eff-
ective magnetic moment; and l/CHIM»reciprocal molar susceptibility.
154
one face of the porphyrin and therefore prevent the formation of the
ir o n (III) /i-oxo dimer upon oxygenation of the ferrous porphyrin.28
For our purposes, this steric hindrance is an advantage in forming 5-
coordinate metalloporphyrins with the nickel and copper imidazolate
complexes rather than 6-coordinate bis-imidazolate complexes. It was
hoped that the F e (III)-Im -C u (II) complex would be especially enlight
ening as a model for cytochrome c oxidase, however the formation of the
nickel and copper imidazolate bridged complexes led to a change in spin
state for the F e (III) center. This is evident in the magnetic and
Mossbauer data for [Fe(C2Cap)(NiIm)](BjjCH22)- The room temperature
magnetic moment of 5.27/xb is too low to correspond to an S=5/2 center
( 5 . 9 2 / z b ) > and too high for an S=3/2 center [ 3 . 8 7 h q ). The spin admix
ture is also evident in the non-linearity of the 1/xm vs. T plot
(Figure 5-14). The high temperature data above 120K are fa irly linear
(Figure 5-15), however, the fact that the iron center is not completely
S=3/2 is reflected in the high g value of 2.32 calculated from this
data. Table 5-10 gives the variable temperature data. The 77K
Mossbauer analysis shows an unsymmetrical quadrupole doublet with
6=0.37mm/s and A E q = 2 .32mm/s. The large quadrupole splitting is
indicative of intermediate spin F e (III) as in Fe(TPP)C104 with
6=0.38mm/s and AEQ=3.48mm/s.42
The copper analogue [Fe^Cap)(Culm)] (Bj i CH^) exhibits the same
spin admixture as well as a small anti ferromagnetic coupling between
the metal centers. Figure 5-16 shows the plot of magnetic moment vs.
temperature for 2.3 to 300K. The room temperature moment of 5.38^tg is
COn
CO CO
CO
Figure 5-13. Schematic drawing of Baldwin's capped porphyrin, abbreviated C2Cap, (from reference
26).
cn
c n
156
similar to that of the nickel complex, however, at low temperatures
the sharp decrease indicates anti ferromagnetic coupling. The solid
curve is the best theoretical f i t with g=2.62, D=-14.9cm_1, and J=-
20.8cirfl. The poor f i t of the curve indicates that the S=3/2 model used
is not completely accurate, however it is closer to the experimental
data than a curve derived from an S=5/2 model. The g value calculated
from the 1/xm v s . T plot (Figure 5-17) is also high at 2.36. The
variable temperature data is given in Table 5-11.
The Mossbauer analysis at 4.2K is unexpected in that i t contains
two quadrupole doublets. The majority of the sample, 62%, has
5=0.40mm/s and AEq=1.20mm/s, parameters typical of high spin ir o n ( III) ,
while the other portion, 38%, has 6=0.36mm/s and AEq=2.50mm/s
indicative of intermediate spin ir o n ( III) . This evidence tends to rule
out the quantum mechanical mixture of S=3/2,5/2 in favor of a thermal
equilibrium of the two spin states. An explanation of why this does
not occur in the nickel analogue is uncertain.
Summary
A series of metalloporphyrin imidazolate bridged binuclear and
trinuclear complexes have been synthesized and characterized. These
include Fe(TPP) (MIm)2, [Fe(TPP) (MIm)2] (Bn CH12) , Mn(TPP) (MIm), and
[Fe(C2Cap)(MIm)] (Bj i CHi 2) , where TPP = tetraphenyl porphyrin, C2Cap =
Baldwin's capped porphyrin, and MIm = the nickel and copper
imidazolate complexes. The diamagnetic nickel complex was employed as
a magnetic blank.
, BM
5 -
...................
4 -
3 -
2 -
0 25 50 75 100 125 150 175 200 225 250 275
Temperature, K
Figure 5-14. Plot of magnetic moment vs. temperature for [Fe(C2Cap)(NiIm)](BuCHi2)'4THF.
90
8 0 -
7 0 -
6 0 -
5 0 - 2
x
\
4 0 -
30 -
2 0 -
▲
0 25 50 75 100 125 150 175 200 225 250 275 300
Temperature, K
Figure 5-15. Plot of reciprocal molar susceptibility vs. temperature for
EFe(C2Cap)(NiIm)](BjiCHi2 ) ‘THF. Solid line is linear least-squares f i t for data above
120K with slope = 0.247, x-intercept = -51.6, and coefficient of correlation = 0.99969.
TEMP MAGSN. C O R fi. C H IG C H IM MUEFF J/C H 1M 159
2.31000 0.07941 1.38234E -03 3.29230E -04 0.4 331 9 3.42107 1.33093
3.03000 0.04341 1.37708E -03 2.41742E -04 0.51937 3.34003 1.92444
3.83000 0.0327S 1.37347E -03 2.14749E -04 0.4 305 3 3.44094 2.32249
3.00000 0.04307 1 .37249E-03 1 .73937E-04 0.3 494 9 3.73945 2.85944
3.S0000 0.04018 I.3 7 0 1 9 E -0 3 1.43734E-04 0.32557 3.78428 3.07131
4.00000 0.03717 I.3 4 9 1 9 E -0 3 1 .3 I0 3 8 E -0 4 0 .3 004 3 3.79490 3.32850
4.99800 0.03313 1.34299E -03 1 .34037E-04 0.24473 3.84374 3.74900
8.00000 0.03003 1.3S448E-03 I.2 0 9 8 4 E -0 4 0.2 408 9 3.92587 4.13122
9.99800 0.02340 1.35409E -03 1.01459E-04 0.2 0 2 2 3 4.02128 4.94472
12.00300 0.02241 1.35249E -03 8.38493E -03 0.1 7 7 2 4 4.12330 3.44114
13.00200 0.01839 1.33039E -03 7.27400E -03 0.1 453 7 4.17434 4.87877
20.00000 0.01475 1.33040E -03 3.43383E -0S 0.1 132 9 4.23700 8.82434
24.99800 0.01237 I.3 4 4 3 0 E -0 3 4.4S210E-0S 0.09344 4.32249 10.49929
30.00000 0.01074 1.34319E -03 3.94489E -0S 0.0 798 3 4.37723 12.32220
34.99800 9.S 7200E -03 1.33979E -03 3.47330E -03 0.07012 4.43047
14.23940
39.99700 8.44800E -03 1.33849E -03 3.08409E -03 0.04241 4.44840
14.02047
44.99200 7.92800E -03 1.33829E -03 2.78044E -05 0.05440 4.30322
17.72802
50.13700 7.30500E -03 I.3 3 4 9 0 E -0 3 2.31902E -03 0.03123 4.33330
19.31913
55.24200 4.80500E -03 1.33430E -03 2.30738E -03 0.04704 4.53883
21.25784
40.34200 4.38700E -03 1.33149E -03 2 .I3 3 I2 E -0 3 0.0 433 9 4.38438
22.94033
44.99800 4 .0 4 !00E-03 1.33049E -03 1.99399E -03 0.04087 4.40941
24.44409
49.94700 3.74300E -03 1.33030E -03 1.84189E -05 0.03822 4.42444
24.14343
73.22300 S .45500E -03 1 . 32442E-03 1.74277E -05 0.03584 4.44490
27.88401
80.38300 5 .2 1 S00E-03 1.32430E -03 I .44 144 6-0 5 0.03384 4.44341
29.53284
90.94700 4.79000E -03 1.31809E -03 1.44493E -05 0.03034 4.49987
32.93591
99.93300 4.42700E -03 1.31249E -03 1.31413E -03 0.02737 4.47738
34.52783
110.41700 4.24200E -03 1 .30744E-03 1.23820E -05 0.02387 4.77992
38.45023
120.73300 3.99100E -03 1.30129E -03 I.I3 4 8 9 E -0 5 0.02382 4.79458
41.94822
130.18300 3 .8 1 300E-03 1.29534E -03 1.0 430 46-03 0.02240 4.82983
44.43213
140.34700 3.44400E -03 1.289336-03 9 .9 333 16-04 0.02102 4.84214
47.35400
141.34700 3.33300E -03 I.2 7 4 7 7 E -0 3 8.77731E -04 0.01873 4.92033
53.37311
180.05000 3 .1 8100E-03 I.2 4 2 4 8 E -0 3 8.09498E -04 0.0 173 8 5.00339
57.32031
199.98300 3.00000E -03 I.2 4 7 9 8 E -0 3 7.39243E -04 0.0 159 9 3.03774
42.32274
219.93000 2.84400E -03 1.231496-03 4 .8 122 36-04 0.01484 5.11019
47.34088
23 9.95000 2 .7 I0 0 0 E -0 3 1.21447E -03 4.30940E -04 0.01384 3.15540
72.20292
239.91700 2.38400E -03 I.I9 7 7 8 E -0 3 3.85744E -04 0.01293 3.18938
77.19008
279.84700 2.48IO O E-03 1.18248E -03 3.47895E -04 0.01220 3.22480
81.92903
29 9.81700 2.39000E -03 1.144346-03 S .I4 2 1 4 E -0 4 0.01137 3.24903
84 .347 23
M u t o ! ■ 0.02370
M o ltc u la r W *lg h t • 1979.88000
01 unagftt11e e o rr» c 1 1o n/T IP <»E-4> • -1338.00000
Table 5-10. Variable temperature magnetic susceptibility data for
[Fe(C2Cap)(NiIm)](B11CH12)-4THF in 10KG magnetic fie ld . TEMP=temp-
erature, K; MAGSN=magnetization of sample and bucket; C0RR=magne-
tization of bucket; CHIG=gram susceptibility; CHIM=molar suscep
t ib ilit y ; MUEFF=effective magnetic moment; and l/CHIM=reciprocal molar
susceptibility.
, BM
5 -
3 -
0 25 50 75 100 125 150 175 200 225 250 275 300
Temperature, K
Figure 5-16. Plot of magnetic moment vs. temperature for [Fe(C2Cap)(CuIm)](BnCHi2 )'THF.
Curve is theoretical best f i t with g = 2.62, D = -14.9, and 0 = -20.8cm'1.
1/Xm
90
8 0 -
7 0 -
50
4 0 -
3 0 -
0 -
0 25 50 75 100 125 150 175 200 225 250 275 300
Temperature, K
Figure 5-17. Plot of reciprocal molar susceptibility vs. temperature for
[Fe(C2Cap)(CuIm)](BuCHi2)'THF. Solid line is linear least-squares f i t for data above
50K with slope = 0.239, x-intercept = -49.4, and coefficient of correlation = 0.99956.
TEHP m G S N . CORR. CM1G CH IH KUEFF 1/CH1M
1 6 2
2 .3 1 0 0 0 0 .0 4 4 7 4 1 .2 6 6 4 1 6 -0 3 1 .3 2 0 7 7 6 -0 4 0 .2 3 4 7 7 2 .0 8 2 7 0 4 .2 3 7 0 7
2 .7 3 0 0 0 0 .0 4 2 1 3 1 .2 8 1 8 6 6 -0 3 1 .2 4 1 5 8 6 -0 4 0 .2 2 0 7 8 2 .2 7 4 3 7 4 .3 2 7 2 3
3 .3 7 0 0 0 0 .0 4 0 0 2 1 .2 8 1 8 7 6 -0 3 1 .1 7 7 4 5 6 -0 4 0 .2 0 7 4 4 2 .4 3 2 2 4 4 ,7 7 4 4 8
4 .0 3 0 0 0 0 .0 3 8 7 4 1 .2 8 0 1 7 6 -0 3 1 .1 3 8 5 7 6 -0 4 0 .2 0 2 5 7 2 .5 6 1 5 3 4 .7 3 6 4 2
4 .5 5 0 0 0 0 .0 3 7 1 6 1 .2 7 3 6 0 6 -0 3 I .0 7 0 7 7 6 -0 4 0 .1 7 4 1 1 2 .6 3 7 7 7 3 .1 3 1 4 8
5 .0 0 0 0 0 0 .0 3 6 2 7 I.2 7 1 0 8 E -0 3 1 .0 6 4 4 0 6 -0 4 0 .1 8 7 4 3 2 .7 5 2 4 4 3 .2 7 8 2 7
5 .5 0 0 0 0 0 .0 3 3 2 5 1 .2 7 0 2 3 6 -0 3 1 .0 3 2 8 1 6 -0 4 0 .1 6 3 8 7 2.8 4 3 7 1 3 .4 3 8 6 0
6 .0 0 0 0 0 0 .0 3 3 8 8 I.2 6 6 7 2 E -0 3 7 .7 1 2 1 7 6 -0 5 0 .1 7 6 5 1 2 .7 1 0 3 4 5 .6 6 5 2 7
7 .0 0 0 0 0 0 .0 3 1 7 5 1 .2 6 6 8 7 6 -0 3 7 .2 6 5 3 7 6 -0 5 0 .1 6 3 0 7 3 .0 3 7 7 8 6 .0 3 7 8 0
8 .0 0 0 0 0 0 .0 2 7 7 6 1 .2 6 3 8 7 E -0 3 8 .72221 E -Q S 0 .1 5 5 4 7 3.15371 6 .4 3 2 0 3
10.00000 0 .0 2 6 7 7 1 .2 6 0 4 7 6 -0 3 7 .8 2 0 5 1 6 -0 5 0 .1 3 7 5 2 3 .3 4 0 4 6 7.1 6 7 1 1
12.00000 0 .0 2 4 0 6 1 .2 5 7 0 0 6 -0 3 6 .7 3 1 0 0 6 -0 5 0 .1 2 3 7 7 3 .4 4 6 8 6 8 .0 7 7 7 7
13.00000 0 .0 2 0 7 8 1 .2 5 3 4 9 6 -0 3 5 .7 9 3 8 9 6 -0 3 0 .1 0 7 2 6 3.38711 7 .3 2 3 1 0
2 0 .0 0 0 0 0 0 .0 1 6 7 7 1 .2 3 0 8 5 6 -0 3 4 .7 7 7 8 5 E -0 5 0 .0 8 5 7 2 3 .7 0 2 8 7 1 1 .6 6 5 7 2
2 5 .0 0 0 0 0 0 .0 1 4 4 4 I .2 4 7 8 9 6 -0 3 4 .0 0 7 1 4 E -0 5 0 .0 7 2 1 2 3 .7 9 7 5 2 1 3 .8 6 4 2 8
3 0 .0 0 0 0 0 0 .0 1 2 7 3 1 .2 4 8 7 2 6 -0 3 3 .4 8 7 7 4 6 -0 3 0 .0 6 2 7 4 3 .8 8 6 0 7 1 3 .8 8 7 3 7
3 3 .0 0 0 0 0 0 .0 1 1 2 7 1 .2 4 7 8 2 6 -0 3 3 .0 4 6 2 5 E -0 3 0 .0 3 5 1 0 3 .7 2 7 2 7 1 8 .1 4 8 6 7
4 0 .0 0 0 0 0 0 .0 1 0 5 6 J . 2 4 6 3 0 6 -0 3 2 .8 3 0 8 5 6 -0 3 0 .0 5 1 2 7 4.0 5 0 7 1 1 7 .4 7 6 4 6
4 5 .0 0 0 0 0 7 .8 2 1 7 0 6 -0 3 1 .2 4 4 2 5 6 -0 3 2 .6 0 7 1 2 E -0 5 0 .0 4 7 3 3 4 .1 2 7 4 0
2 1 .1 2 5 7 6
50.0 1 5 0 0 7 .2 3 3 0 0 6 -0 3 1 .2 4 1 3 7 6 -0 3 2 .4 2 7 0 0 6 -0 5 0 .0 4 4 1 8 4 .2 0 4 0 5
22.6 3 1 7 5
3 5 .2 8 2 0 0 8 .4 8 0 0 0 6 -0 3 1 .2 3 7 1 7 6 -0 3 2 .2 0 0 8 5 6 -0 5 0 .0 4 0 1 5 4 .2 1 3 2 5
2 4 .7 0 6 1 2
6 0 .3 6 0 0 0 8 .2 7 3 3 0 6 -0 3 1 .2 3 7 9 1 6 -0 3 2 .I3 8 4 1 E - 0 5 0 .0 3 7 0 4 4 .3 4 1 5 6
2 3 .6 1 0 3 8
64.7 7 0 0 0 7 .7 3 7 0 0 E -0 3 1 .2 3 7 1 2 6 -0 3 2 .0 3 6 4 3 E -Q 5 0 .0 3 7 2 4 4 .3 7 7 7 4
2 6 .8 5 0 4 4
7 0 .0 0 0 0 0 7 .6 0 0 0 0 6 -0 3 1 .2 3 5 8 7 6 -0 3 1 .7 3 4 3 7 E -0 S 0 .0 3 5 4 3 4 .4 5 4 1 6
2 8 .2 1 7 8 5
75.3 6 7 0 0 7 .2 7 5 0 0 E -0 3 1 .2 3 3 7 8 6 -0 3 1 .8 3 6 2 3 E -0 5 0 .0 3 3 7 0 4 .5 0 7 1 7
2 7 .6 7 0 8 6
8 0 .3 8 3 0 0 6 .7 8 8 3 0 E -0 3 1 .2 3 1 6 2 E -0 3 1 .7 4 7 7 4 6 -0 5 0 .0 3 2 1 7 4.54771
31.0813 0
7 0 .0 0 0 0 0 6 .5 7 6 0 0 6 -0 3 1 .2 2 7 7 7 E -0 3 1 .6 2 5 5 7 E -0 5 0 .0 2 7 7 7 4 .6 4 5 1 8
33.3576 0
7 7 .7 1 7 0 0 6 .1 8 3 3 0 6 -0 3 1 .2 2 3 1 7 E -0 3 1 .5 0 7 6 3 6 -0 5 0 .0 2 7 8 7 4 .7 2 1 0 7
35.8 5 2 3 0
110 .800 00 5 .7 9 6 7 0 6 -0 3 1 .2 1 6 4 2 E -0 3 1 .3 7 2 1 7 6 -0 5 0 .0 2 5 8 5 4 .7 8 6 1 3
38.6 8 3 8 0
120 .117 00 S .4 7 1 7 0 E -0 3 1 .2 1 1 6 1 6 -0 3 1 .3 0 0 7 3 6 -0 5 0 .0 2 4 2 3 4 .8 2 5 2 7
4 1 .2 5 7 0 2
130 .483 00 5 .2 3 3 0 0 E -0 3 1 .2 0 6 6 2 6 -0 3 1 .2 2 3 8 2 6 -0 5 0 .0 2 2 8 7 4 .8 8 5 6 4
43.71881
140 .150 00 5 .0 4 5 0 0 6 -0 3 1 .2 0 0 7 7 6 -0 3 1 .1 6 8 4 4 6 -0 5 0 .0 2 1 8 9 4 .9 5 3 8 3
4 5 .6 7 4 0 2
161 ,450 00 4 .5 8 2 0 0 6 -0 3 1 .1 8 5 5 1 6 -0 3 1 .0 3 2 3 6 6 -0 5 0 .0 1 9 4 8 5 .0 1 6 2 6
5 1 .3 1 3 7 7
180 .167 00 4 .3 2 3 0 0 E -0 3 1 .1 7 3 5 9 6 -0 3 7 .5 7 2 6 4 6 -0 6 0 .0 1 8 1 5 5.1 1 5 3 1
5 3 .0 6 6 7 2
2 0 0 .0 0 0 0 0 4 .0 4 6 7 0 6 -0 3 1 .1 S 7 8 9 E -0 3 8 .7 7 4 4 6 6 -0 6 0 .0 1 6 7 4 5 .1 7 3 8 3
5 7 .7 0 7 4 4
2 1 7 .7 6 7 0 0 3 .8 1 3 3 0 6 -0 3 1 .1 4 3 4 8 6 -0 3 8 .1 1 4 7 3 6 -0 6 0 .0 1 5 5 8 5 .2 3 5 6 4
64.17641
2 3 7 .7 1 7 0 0 3 .6 0 0 0 0 6 -0 3 1 .1 2 6 4 1 6 -0 3 7 .5 1 8 5 0 6 -0 6 0 .0 1 4 5 2 5 .2 7 7 6 2
6 8 .8 3 5 7 0
2 5 7 .8 6 7 0 0 3 .4 2 1 7 0 6 -0 3 1 .1 1 2 3 4 6 -0 3 7 .0 1 7 3 1 E -0 6 0 .0 1 3 6 4 5 .3 2 5 1 7
7 3 .2 8 7 0 4
277 .8 6 7 0 0 3 .2 5 8 3 0 6 -0 3 1 .0 7 8 7 2 6 -0 3 6 .5 6 4 0 6 6 -0 6 0 .0 1 2 8 3 5 .3 6 0 8 0
7 7 .8 8 4 2 8
2 7 7 .7 8 3 0 0 3 .1 0 1 7 0 6 -0 3 1 .0 8 4 0 5 6 -0 3 6 .1 3 2 6 7 E -0 6 0 .0 1 2 0 7 5 .3 8 0 7 2
82.8040 1
M ae* o f ta m p 11 M o )*C w l*r U t ig h t - 1 7 6 8 .3 5 0 0 0
D la ia a g n M ic c o r r - * c t( o n / T ! 7 <»E-6> • -1 2 3 2 .0 0 0 0 0
Table 5-11. Variable temperature magnetic susceptibility data for
[FetCgCap)(Culm)](BjjCHig)*THF in 10KG magnetic fie ld . TEMP=temp-
erature, K; MAGSN=magnetization of sample and bucket; CORR=magne-
tization of bucket; CHIG=gram susceptibility; CHIM=molar suscep
t ib ilit y ; MUEFF=effective magnetic moment; and l/CHIM=reciprocal molar
susceptibility.
163
The change in magnetic susceptibility as a function of temperature
over the range of 6 to 300K has been studied for each of these
compounds. For the iro n (II) bis-imidazolate complexes, the nickel
complex shows the expected diamagnetism, while the copper complex
exhibits a slight anti ferromagnetic coupling between the copper
centers, which could be either an intra- or inter-molecular
interaction. The iro n (III) bis-imidazolate complexes contain a low
spin iron center which is ferromagnetically coupled to the copper
centers with a coupling constant, J=10cm'l. The copper centers are
also weakly coupled to one another antiferromagnetically with J=-
0.35cm‘ l. An x-ray crystal structure of this complex has also been
presented which indicates the Cu-Cu interaction may be intermolecular.
The 5-coordinate manganese complexes contain high spin Mn(II)
which poses as a spin model for cytochrome c oxidase and in the copper
analogue the anti ferromagnetic coupling is weak, J=-6cm“l. The
Fe( 111)/Cu(II) complex using the capped porphyrin was expected to
present an excellent model for cytochrome c oxidase, however, the
presence of an S=3/2,5/2 spin admixture complicates the interpretation
of the magnetic data. In any case the anti ferromagnetic coupling in
the copper complex is weak at best and i f a to tally S=3/2 model is
used, the best f i t gives J=-20.8cm'*.
It is obvious that in this series of cytochrome c oxidase models,
the imidazolate bridge is not capable of mediating any coupling between
two metal centers other than weak coupling. It is noteworthy that the
ir o n (III) bis-imidazolate complex displays ferromagnetic coupling which
is unprecedented in imidazolate bridged species. This work supports
the proposal that strong anti ferromagnetic coupling (-J>200cm“l)
between the F e (III) and Cu(II) sites in cytochrome c oxidase cannot be
mediated by an imidazolate bridge. This does not however rule out
imidazolate as a bridging ligand in the active site of cytochrome c
oxidase, since there are alternative explanations for the EPR silence
and magnetic susceptibility of the enzyme.
165
References
1. Blair, D. F.; Martin, C. T.; Gelles, J.; Wang, H.; Brudvig, G. W.;
Stevens, T. H.; Chan, S. I. Chemica Scripta 1983, 21, 43-53.
2. Stevens, T. H.; Chan, S. I. J. Biol. Chem. 1981, 256, 1069-1071.
3. Palmer, G.; Babcock, G. T.; Vickery, L. E. Proc. Natl. Acad. Sci.
1976, 73, 2206-2210.
4. Kolks, G.; Lippard, S. J. J. Am. Chem. Soc. 1977, 99, 5804-5806.
5. Katz, R. N.; Kolks, G.; Lippard, S. J. Inorg. Chem. 1980, 19,
3845-3847.
6. Haddad, M. S.; Hendrickson, D. N. Inorg. Chem. 1978, 17, 2622-
2630.
7. Haddad, M. S.; Duesler, E. N.; Hendrickson, D. N. Inorg. Chem.
1979, 18, 141-148.
8. Kolks, G.; Frihart, C. R.; Coughlin, P. K.; Lippard, S.
J. Inorg. Chem. 1980, 20, 2933-2940.
9. Landrum, J. T.; Reed, C. A.; Hatano, K .; Scheidt, W . R.
J. Am. Chem. Soc. 1978, 100, 3231-3234.
10. Landrum, J. T.; Grimmett, D.; Haller, K. J.; Scheidt, W . R.;
Reed, C. A. J. Am. Chem. Soc. 1981, 103, 2640-2650.
11. Prosperi, T.; Tomlinson, A. A. G. J. Chem. Soc.,
Chem. Common. 1979, 196-197.
12. Kovacs, D.; Shepherd, R. E. J. Inorg. Biochem. 1979, 10, 67-88.
13. Davis, W . M.; Dewan, J. C.; Leppard, S. J. Inorg. Chem. 1981, 20,
2928-2932.
14. Cutler, A. C.; Brittain, T.; Boyd, P. D. W . J. Inorg. Biochem.
1985, 24, 199-209.
15. Saxton, R. J.; Wilson, L. J. J. Chem. Soc., Chem. Commun. 1984,
359-361.
16. Dessens, S. E.; M errill, C. L.; Saxton, R. J.; Ila ria , J r., R. L.;
Lindsey, J. W.; Wilson, L. J. J. Am. Chem. Soc. 1982, 104, 4357-
4361.
17. Chunplang, V.; Wilson, L. J. J. Chem. Soc., Chem. Commum.1985,
1761-1763.
166
18. Chunplang, V. Ph.D. Thesis, Rice University, May 1985.
19. Atkins, R.; Brewer, G.; Kokot, E.; Mockler, G. M.; Sinn, E.
Inorg. Chem. 1985, 24, 127-134.
20. Brewer, G.; Sinn, E. Inorg. Chim. Acta 1984, 87, L41-L43.
21. Brewer, C. T . ; Brewer, G. J. Inorg. Biochem. 1986, 26, 247-255.
22. Gonzalez, B.; Kouba, J.; Yee, S.; Reed, C. A.; Kirner, J. F.;
Scheidt, W . R. J. Am. Chem. Soc. 1975, 97, 3247-3249.
23. Kirner, J. F.; Reed, C. A.; Scheidt, W . R. J. Am. Chem. Soc. 1977,
99, 2557-2563.
24. Kirner, J. F.; Reed, C. A.; Scheidt, W . R. J. Am. Chem. Soc. 1977,
99, 1093-1101.
25. Reed, C. A.; Mashiko, T.; Scheidt, W . R.; Spartalian, K .; Lang, G.
J. Am. Chem. Soc. 1980, 102, 2302-2306.
26. Gupta, G. P.; Lang, G.; Lee, Y. J.; Scheidt, W . R.; Shelly, K.;
Reed, C. A. Inorg. Chem. 1987, 26, 3022-3030.
27. Almog, J.; Baldwin, J. E.; Dyer, R.; L.; Peters, M.
J. Am. Chem. Soc. 1975, 97, 226-227.
28. Almog, J.; Baldwin, J. E.; Juff, J. J. Am. Chem. Soc. 1975, 97,
227-228.
29. Handbook of Chemistry and Physics, 61st ed.; CRC: Boca Raton,
1973; pp E123-El36.
30. Mulay, L. N. In Theory and Applications of MolecuTar
Paramagnetism; Boudreaux, E. A., Ed.; John Wiley & Sons: New York,
1976; Chapter 9.
31. Eaton, S. S.; Eaton, G. R. Inorg. Chem. 1980, 19, 1096-1098.
32. O'Connor, C. J. In Progress in Inorganic Chemistry; Lippard, 0.,
Ed.; John Wiley & Sons: New York, 1982; Vol. 29, pp 203-284.
33. Scheidt, W . R.; Reed, C. A. Chem. Rev. 1981, 81, 543-555.
34. Sams, J. R.; Tsin, T. B. In The Porphyrins; Dolphin, D., Ed.;
Academic: New York, 1979; Vol. IV, Chapter9.
35. Collman, J. P.; Hoard, J. L.; Kim, N.; Lang, G.; Reed, C. A.
J. Am . Chem. Soc. 1975, 97, 2676-2681.
157
36. Drago, R. S. Physical Methods in Chemistry; W . B. Saunders:
Philadelphia, 1977; Chapter 13.
37. Kahn, 0. Com m . Inorg. Chem. 1984, 3, 105-132.
38. Pei, Y.; Journaux, Y.; Kahn, 0. Inorg. Chem. 1988, 27, 399-404.
39. Vos, G.; Haasnoot, J. G.; Verschoor, G. C.; Feedijk, J.;
Schaminee, R. E. L. Inorg. Chim. Acta. 1985, 105, 31-39.
40. Haase, W.; Gehring, S. J. Chem. Soc., Dalton Trans. 1985, 2609-
2613.
41. Brewer, G.; Koch, C. A.; Reed, C. A.; Scheidt, W . R. Manuscript in
preparation.
42. Reed, C. A.; Mashiko, T.; Bentley, S. P.; Kastner, M. E.;
Scheidt, W . R.; Spartalian, K.; Lang, G. J. Am. Chem. Soc. 1979,
101, 2948-2958.
168
Selected Bibliography
Almog, J.; Baldwin, J. E.; Dyer, R.; L.; Peters, M.
J. Am. Chem. Soc. 1975, 97, 226-227.
Almog, J.; Baldwin, J. E.; Juff, J. J. Am. Chem. Soc. 1975, 97,
227-228.
Aoi, N.; Takano, Y.; Ogino, H.; Matsubayashi, G.; Tanaka, T.
J. Chem. Soc., Chem. Commun. 1985, 703-704.
Armstrong, F.; Shaw, R. W.; Beinert, H. Biochim. Biophys. Acta
1983, 722, 61-71.
Atkins, R.; Brewer, G.; Kokot, E.; Mockler, G. M.; Sinn, E.
Inorg. Chem. 1985, 24, 127-134.
Babcock, G. T.; Callahan, P. M.; Ondrias, M. R.; Salmeen, I.
Biochemistry 1981, 20, 959-966.
Babcock, G. T.; Vickery, L. E.; Palmer, G. J. Biol. Chem. 1976,
251, 7907-7919.
Beaven, G. R.; Holiday, E. R.; Johnson, E. A.; E llis , B.;
Mamalis, P.; Petrow, V.; Sturgeon, B. J. Pharm. Pharmacol. 1949, 1,
957-970.
Berry, K. J.; Clark, P. E.; Gunter, M. J.; Murray, K. S.
Nouv. J. Chim. 1980, 4, 581-585.
Birker, J. J. M. W . L.; Hendricks, H. M. J.; Reedijk,
J. Inorg. Chim. Acta 1981, 55, LI7-18.
Blair, D. F.; Martin, C. T.; Gelles, J.; Wang, H.; Brudvig, G. W.;
Stevens, T. H.; Chan, S. I. Chem. Scripta 1983, 21, 43-53.
Bose, K. S.; Sharma, B. C.; Patel, C. C. J. Inorg. Nucl. Chem.
1970, 32, 1742-1743.
Brunori; M.; Antonini, G.; Molatesta, F.; Sarti, P.; Wilson, M. T.
In Advances in Inorganic Chemistry: Heme Proteins', Eichorn, G. L.;
M a rzilli, L. G., Eds.; Elsevier: New York, 1988; Vol.7, Chapter 3.
Brewer, C. T.; Brewer, G. J. Inorg. Biochem. 1986, 26, 247-255.
Brewer, G.; Sinn, E. Inorg. Chim. Acta 1984, 87, L41-L43.
Buchler, J. W . In Porphyrins Dolphin, D., Ed. Academic: New York,
1978; Vol. 1, Chapter 10, pp 389-483.
169
Buckingham, D. A.; Gunter, M. J.; Mander, L. N. J. Am. Chem. Soc.
1978, 100, 2899-2901.
Buse, G.; Meinecke, L.; Bruch, B. J. Inorg. Biochem. 1985, 23,
149-153.
Caughey, W . S. In Inorganic Biochemistry; Eichorn, G., Ed.;
Elsevier: Amsterdam, 1973; Vol. 2, Chapter 24.
Chan, S. I . ; Brocian, D. F.; Brudvig, G. W.; Morse, R. H.;
Stevens, T. H. In Frontiers of Biological Energetics; Dutton, P. L.;
Leigh, J r., J. S.; Scarpa, A., Eds.; Academic: New York, 1978; Vol.2,
pp 883-888.
Chang, C. K.; DiNello, R. K .; Dolphin, D. In Inorganic Syntheses,
Busch, D. H., Ed.; John Wiley & Sons: New York, 1980; Vol. XX, pp 147-
155.
Chang, C. K.; Koo, M. S.; Ward, B. J. Chem. Soc., Chem. Common.
1982, 716-719.
Cheng, R. J.; Latos-Grazynski, L.; Balch, A. L. Inorg. Chem. 1982,
21, 2412-2418.
Cense, J. M.; Le Quan, R. M. Tetd. Letts. 1979, 39, 3725-3728.
Chunplang, V.; Wilson, L. J. J. Chem. Soc., Chem. Commun. 1985,
1761-1763.
Cline, J.; Reinhammar, B.; Jensen, P.; Venters, R.; Hoffman, B. M.
J. Biol. Chem. 1983, 258, 5124-5128.
Collman, J. P. Acc. Chem. Res. 1977, 10, 265-272.
Collman, J. P.; Brauman, J. I.; Collins, T. J.; Iverson, B. L.;
Lang, G.; Pettman, R. B.; Sessler, J. L.; Walters, M. A. J. Am. Chem.
Soc. 1983, 105, 3038-3052.
Collman, J. P.; Brauman, J. I . ; Doxsee, K. M.; Halbert, T. R.;
Hayes, S. E.; Suslick, K. S. J. Am. Chem. Soc. 1978, 100, 2761- 2766.
Collman, J. P.; Gagne, R. R.; Reed, C. A.; Halbert, T. R.;
Lang, G.; Robinson, W . T. J. Am. Chem. Soc. 1975, 97, 1427-1439.
Collman, J. P.; Reed, C. A. J. Am. Chem. Soc. 1973, 95, 2048-2049.
Cordes, M. M.; Walter, J. L. Spectrochim. Acta 1968, 24, 1421-
1435.
Cotton, F. A.; Wilkinson, G. Anvanced Inorganic Chemistry, 3rd
ed.; Interscience: New York, 1972.
170
Csoregh, I . ; Kierkegaard, P.; Norrestam, R. Acta Cryst. 1975, B31,
314-317.
Cutler, A. C.; Brittain, T.; Boyd, P. D. W . J. Inorg. Biochem.
1985, 24, 199-209.
Davis, A. R.; Einstein, F. W . B.; Curtis, N. F.; Mattin, J. W . L.
J. Am. Chem. Soc. 1978, 100, 6258-6260.
Davis, W . M.; Dewan, J. C.; Leppard, S. J. Inorg. Chem. 1981, 20,
2928-2932.
Deatherage, J. F.; Henderson, R.; Capaldi, R. A. Chem. Scripts
1983, 21, 35-39.
Dessens, S. E.; M errill, C. L.; Saxton, R. J.; Ila ria , J r., R. L.;
Lindsey, J. W.; Wilson, L. J. J. Am. Chem. Soc. 1982, 104, 4357-4361.
Drago, R. S. Physical Methods in Chemistry; W . B. Saunders:
Philadelphia, 1977; Chapter 13.
Eaton, S. S.; Eaton, G. R. Inorg. Chem. 1980, 19, 1096-1098.
Einarsdottir, 0.; Caughey, W . S. Biochem. Biophys. Res. Commun.
1985, 129, 840-847.
E llio tt, C. M. Anal. Chem. 1980, 52, 666-668.
E llio tt, C. M.; Akabori, K. J. Am . Chem. Soc. 1982, 104, 2671-
2674.
E llio tt, C. M.; Jain, N. C.; Cranmer, B. K.; Hamburg, A. W .
Inorg. Chem. 1987, 26, 3655-3659.
English, D. R.; Hendrickson, W . N.; Suslick, K. S. Inorg. Chem.
1983, 22, 368-370.
Fleischer, E. B.; M iller, C. K.; Webb, L. E. J. Am. Chem. Soc.
1964, 86, 2342-2347.
Frey, T. G.; Kuhn, L. A.; Leigh,Jr., J. S.; Costello, M. J.;
Chan, S. H. P. J. Inorg. Biochem. 1985, 23, 155-162.
Ghosh, S. P. J. Indian Chem. Soc. 1951, 27, 710-712.
Glick, M. D.; Cohen, G. H.; Hoard, J. L. J. Am. Chem. Soc. 1967,
89, 1996-1998.
Gonzalez, B.; Kouba, J.; Yee, S.; Reed, C. A.; Kirner, J. F.;
Scheidt, W . R. J. Am . Chem. Soc. 1975, 97, 3247-3249.
171
i Goodgame, M.; Haines, L. I. B. J. Chem. Soc. (A) 1966, 174-177.
Gordon, A. J.; Ford, R. A. The Chemists Companion, John Wiley &
Sons: New York, 1972.
j Gottwald, L. K.; Ullman, E. F. Tetd. Letts. 1969, 36, 3071-3074.
!
Gunter, M. J.; Berry, K. J.; Murray, K. S. J. Am. Chem. Soc. 1984,
106, 4227-4235.
1 Gunter, M. J.; Mander, L. N. J. Org. Chem. 1981, 46, 4792-4795.
i
1 Gunter, M. J.; Mander, L. N.; Murray, K. S. J.C.S. Chem Common.
: 1981, 799-801.
i
j Gunter, M. J.; Mander, L. N.; McLaughlin, G. M.; Murray, K. S.;
! Berry, K. J.; Clark, P. E.; Buckinghan, D. A. J. Am. Chem. Soc. 1980,
j 102, 1470-1473.
j Gunter, M. J.; Mander, L. N.; Murray, K. S.; Clark, P. E.
! J. Am. Chem. Soc. 1981, 103, 6784-6787.
i
i
Gunter, M. J.; McLaughlin, G. M.; Berry, K. J.; Murray, K. S.;
Irving, M.; Clark, P. E. Inorg. Chem. 1984, 23, 283-300.
Gupta, G. P.; Lang, G.; Lee, Y. J.; Scheidt, W . R.; Shelly, K.;
. Reed, C. A. Inorg. Chem. 1987, 26, 3022-3030.
, Gupta, G. P.; Lang, G. Scheidt, W . R.; Geiger, D. K .; Reed, C. A.
I J. Chem. Phys. 1986, 85, 5212-5220.
Haase, W.; Gehring, S. J. Chem. Soc. Dalton 1985, 2609-2613.
Haddad, M. S.; Duesler, E. N.; Hendrickson, D. N. Inorg. Chem.
1979, 18, 141-148.
i
! Haddad, M. S.; Hendrickson, D. N. Inorg. Chem. 1978, 17, 2622-
, 2630.
| Hagen, W . R. Biochim. Biophys. Acta 1982, 702, 82-98.
Hamilton, W . C.; Ibers, J. A. Hydrogen Bonding in Solids
W . A. Benjamin: New York, 1968, Chapter 1.
Harel, Y.; Felton, R. H. J.C.S. Chem. Commun. 1984, 206-208.
! Hashimoto, T.; Dyer, R. L.; Crossley, M. J.; Baldwin, J. E.;
' Basolo, F. J. Am. Chem. Soc. 1982, 104, 2101-2109.
172
Hatfield, W . E.; E llio tt, C. M.; Ensling, J.; Akabori, K.
Inorg. Chem. 1987, 26, 1930-1933.
Hendricks, H. M. J.; Birker, P. J. M. W . L.; van Rijn, J.;
Verschoor, G. C.; Reedijk, J. J. Am. Chem. Soc. 1982, 104, 3607-3617.
Holm, R. H. Acc. Chem. Res. 1977, 10, 427-434.
Ibers, J. A.; Holm, R. H. Science, 1980, 209, 223-235.
Ingraham, L. L.; Meyer, D. L. Biochemistry of Dioxygen; Plenum:
New York, 1985; Chapters 9 and 10.
Inoue, M.; Kishita, M.; Kubo, M. Inorg. Chem. 1965, 4, 626-629.
James, B. R. In The Porphyrins, Dolphin, D., Ed.; Academic:
New York, 1978; Vol. 5, Chapter 6.
Jameson, G. B.; Ibers, J. A. Comments Inorg. Chem. 1986, 97-126.
Jayaraj, K.; Gold, A.; Toney, G. E.; Helms, J. H.; Hatfield, W . E.
Inorg. Chem. 1985, 25, 3516-3518.
Kadenbach, B. Angew. Chem., Int. Ed. Engl. 1983, 22, 275-283.
Kahn, 0. Com m . Inorg. Chem. 1984, 3, 105-132.
Katz, R. N.; Kolks, G.; Lippard, S. J. Inorg. Chem. 1980, 19,
3845-3847.
Kent, T. A.; Young, L. J.; Palmer, G.; Fee, J. A.; Munck, E.
J. Biol. Chem. 1983, 258, 8543-8546.
King, T. E.; O rii, Y.; Chase, B.; Okunuki, K., Eds. Cytochrome
Oxidase; Elsevier: New York, 1979.
Kirner, J. F.; Reed, C. A.; Scheidt, W . R. J. Am. Chem. Soc. 1977,
99, 1093-1101.
Kirner, J. F.; Reed, C. A.; Scheidt, W . R. J. Am. Chem. Soc. 1977,
99, 2557-2563.
Kolks, G.; Frihart, C. R.; Coughlin, P. K.; Lippard, S.
J. Inorg. Chem. 1980, 20, 2933-2940.
Kolks, G.; Lippard, S. J. J. Am. Chem. Soc. 1977, 99, 5804-5806.
Kovacs, D.; Shepherd, R. E. J. Inorg. Biochem. 1979, 10, 67-88.
173
Krim, S. In Vibrational Spectra and Structure; Durig, J. R., Ed.;
Elsevier: New York, 1987; Vol. 16, Chapter 1.
Kubas, G. J. Inorg. Synth. 1979, 19, 90-92.
Landrum, J. T.; Grimmett, D.; Haller, K. J.; Scheidt, W . R.;
Reed, C. A. J. Am . Chem. Soc. 1981, 103, 2640-2650.
Landrum, J. T.; Reed, C. A.; Hatano, K.; Scheidt, W . R.
J. Am. Chem. Soc. 1978, 100, 3231-3234.
Larsen, N. G.; Boyd, P. D. W.; Rodgers, S. 0.; Wuenschell, G. E.;
Koch, C. A. Rasmussen, S.; Tate, J. R.; Erler, B. S.; Reed, C. A.
J. Am. Chem. Soc. 1986, 108, 6950-6960.
Laskowski, E. J.; Frandel, R. B.; Gillum, W . 0.;
Papaefthymiou, G. C.; Renaud, J.; Ibers, J. A.; Holm, R. H.
J. Am. Chem. Soc. 1978, 100, 5322-5337.
Lecas, A.; Levisalles, J.; Renko, Z.; Rose, E. Tetd. Letts. 1984,
25, 1563-1566.
Lexa, D.; Momenteau, M.; Saveant, J. M.; Xu, F. Inorg. Chem. 1985,
24, 122-127.
Li, P. M.; Gelles, J.; Chan, S. I . ; Sullivan, R. J.; Scott, R. A.
Biochemistry 1987, 26, 2091-2095.
Lindsey, J. J. Org. Chem. 1980, 45, 5215.
Malmstrom, B. G. In Metal Ion Activation of Dioxygen;
Spiro, T. G;, Ed.; John Wiley & Sons: New York, 1980; Chapter 5.
Malmstrom, B. G. Quart. Rev. Biophys. 1973, 6, 384-431.
Mashiko, T.; Marchon, J. C.; Musser, D. T.; Reed, C. A.; Kastner,
M. E.; Scheidt, W . R. J. Am. Chem. Soc. 1979, 101, 3653-3655.
Mashiko, T.; Reed, C. A.; Haller, K. J.; Kastner, M. E.;
Scheidt, W . R. J. Am. Chem. Soc. 1981, 103, 5758-5767.
Mispelter, J.; Momenteau, M.; Lavalette, D.; Lhoste, J. M.
J. Am. Chem. Soc. 1983, 105, 5165-5166.
Miyamoto, T. K .; Tsuzuki, S.; Hasegawa, T.; Sasaki, Y.
Chem. Letts. 1983, 1587-1588.
Momenteau, M.; Mispelter, J.; Loock, B.; Bisagni, E. J. Chem. Soc.
Perkin Trans. 1983, 189-196.
174
Momenteau, M.; Mispelter, J.; Loock, B.; Lhoste, J. M.
J. Chem. Soc. Perkin Trans. 1985, 61-70.
Morgenstern-Badarau, I . ; Wickman, H. H. Inorg. Chem. 1985, 24,
1889-1892.
Morgenstern-Badarau, I . ; Cocco, D.; Desideri, A.; Rotilio, 6.;
Jordanov, J.; Dupre, N. J. Am . Chem. Soc. 1986, 108, 300-302.
Morpurgo, G. 0.; Mosini, V.; Porta, P.; Dessy, G.; Fares, V.
J. Chem. Soc. Dalton Trans. 1981, 111-117.
Mulay, L. N. In Theory and Applications of Molecular
Paramagnetism; Boudreaux, E. A., Ed.; John Wiley & Sons: New York,
1976; Chapter 9.
Murray, K. S. Coord. Chem. Rev. 1974, 12, 1-35.
Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 4th ed.; John Wiley & Sons: New York 1986.
Naqui, A.; Powers, L.; Lundeen, M.; Chance, B. Biophys. J. 1987,
51, 312a.
Nyquist, R. A.; Kagel, R. 0. Infrared Spectra of Inorganic
Compounds, Academic: New York, 1971.
O'Connor, C. J. In Progress in Inorganic Chemistry; Lippard, J.,
Ed.; John Wiley & Sons: New York, 1982; Vol. 29, pp 203-284.
Okawa, H.; Kanda, W.; Kida, S. Chem. Letts. 1980, 1281-1284.
Palmer, G. Pure Appl. Chem. 1987, 59, 749-758.
Palmer, G.; Babcock, G. T.; Vickery, L. E. Proc. Natl. Acad. Sci.
1976, 73, 2206-2210.
Patch, M. A. Ph.D. Thesis, University of Southern California,
August, 1988.
Pei, Y.; Journaux, Y.; Kahn, 0. Inorg. Chem. 1988, 27, 399-404.
Peisach, J. In Frontiers of Biological Energetics; Dutton, P. L.;
Leigh, Jr., J. S.; Scarpa, A., Eds.; Academic: New York, 1978; Vol 2,
pp 873-881.
Prosperi, T.; Tomlinson, A. A. G. J. Chem. Soc., Chem. Commun.
1979, 196-197.
175
Powers, L.; Chance, B.; Ching, Y.; Angiolillo, P. Biophys. J.
1981, 34, 465-498.
Reed, C. A.; Landrum, J. T. FEBS Lett. 1979, 106, 265-267.
Reed, C. A.; Mashiko, T.; Bentley, S. P.; Kastner, M. E.;
Scheidt, W . R.; Spartalian, K.; Lang, G. J. Am. Chem. Soc. 1979, 101,
2948-2958.
Reed, C. A.; Mashiko, T.; Scheidt, W . R.; Spartalian, K.; Lang, G.
J. Am. Chem. Soc. 1980, 102, 2302-2306.
Richardson, J. S.; Thomas, K. A.; Rubin, B. H.; Richardson, D. C.
Proc. Natl. Acad. Sci. 1975, 72, 1349-1353.
Rodgers, S. J.; Koch, C. A.; Tate, J. R.; Reed, C. A.;
Eigenbrot, C. W.; Scheidt, W . R. Inorg. Chem. 1987, 26, 3647-3649.
Rusnak, F. M.; Munck, E.; Nitsche, C. I . ; Zimmerman, B. H.;
Fee, J. A. J. Biol. Chem. 1987, 262, 16328-16332.
Sams, J. R.; Tsin, T. B. In The Porphyrins; Dolphin, D., Ed.;
Academic: New York, 1979; Vol. 4, Chapter 9.
Salomon, R. G.; Kochi, J. K. J. Am. Chem. Soc. 1973,95, 1889-1897.
Saxton, R. J.; Olson, L. W.; Wilson, L. J. J. Chem. Soc., Chem.
Commun. 1982, 984-986.
Saxton, R. J.; Wilson, L. J. J. Chem. Soc., Chem. Commun. 1984,
359-361.
Schauer, C. K.; Akabori, K.; E llio tt, C. M.; Anderson, 0. P.
J. Am. Chem. Soc. 1984, 106, 1127-1128.
Scheidt, W . R. Acc. Chem Res. 1977, 10, 339-345.
Scheidt, W . R.; Haller, K. J.; Hatano, K. J. Am. Chem. Soc. 1980,
102, 3017-1021.
Scheidt, W . R.; Lee, Y. J.; Luangdilok, W.; Haller, K. J.;
Anzai, K .; Hatano, K. Inorg. Chem. 1983, 22, 1516-1522.
Scheidt, W . R.; Reed, C. A. Chem. Rev. 1981, 81, 543-555.
Scott, R. A.; Schwartz, J. R.; Cramer, S. P. In Biological and
Inorganic Copper Chemistry; Karlin, K. D.; Zubieta, J., Eds.; Adenine:
New York, 1985; pp 41-52.
Sekine, M.; Hata, T. J. Org. Chem. 1983, 48, 3011-3014.
176
Sekine, M.; Masuda, N.; Mata, T. Tetrahedron 1985, 41, 5445-5453.
Seiter, C. H. A.; Angelos, S. G. Proc. Natl. Acad. Sci. 1980, 77,
1806-1808.
Seiter, C. H. A.; Angelos, J r., S. G.; Perrault, R. A.
In Frontiers of Biological Energetics; Dutton, P. L.; Leigh, J r., J.
S.; Scarpa, A., Eds.; Academic: New York, 1978; Vol. 2, pp 897-903.
Serr, B. R.; Headford, C. E. L.; E llio tt, C. M.; Anderson, 0. P.
J. Chem. Soc., Chem. Commun. 1988, 92-94.
Shaw, R. W.; Rife, J. E.; O'Leary, M. H.; Beinert, H.
J. Biol. Chem. 1981, 256, 1105-1107.
Smith, K. M. In Porphyrins and Metalloporphyrins; Smith, K. M.,
Ed.; Elsevier Scientific: New York, 1975.
Sorrell, T. N. Inorg. Synth. 1980, 20, 161-169.
Steffens, G. C. M.; Biewald, R.; Buse, G. fur. J. Biochem. 1987,
164, 295-300.
Stevens, T. H.; Chan, S. I. J. Biol. Chem. 1981, 256, 1069-1071.
Stevens, T. H.; Martin, C. T.; Wang, H.; Brudvig, G. W.;
Scholes, C. P.; Chan, S. I. J. Biol. Chem. 1982, 257, 12106-12113.
Storm, C. B.; Teklu, Y. J. Am . Chem. Soc. 1972, 94, 1745-1747.
Storm, C. B.; Teklu, Y.; Sokoloski, E. A. N. Y. Acad. Sci. 1973,
206, 631-640.
Stryer, L. Biochemistry; W . H. Freeman: San Francisco, 1981.
Tweedle, M. F.; Wilson, L. J.; Garcia-Iniguez, L.; Babcock, G. T.;
Palmer, G. J. Biol. Chem. 1978, 253, 8065-8071.
Van Gelder, B. F.; Beinert, H. Biochim. Biophys. Acta 1969, 189,
1-24.
Vos, G.; Haasnoot, J. G.; Verschoor, G. C.; Feedijk, J.;
Schaminee, R. E. L. Inorg. Chim. Acta. 1985, 105, 31-39.
Wikstrom, M.; Krab, K.; Saraste, M. Cytochrome Oxidase,
A Synthesis; Academic: New York, 1981.
Wikstrom, M.; Saraste, M.; Penttila, T. In The Enzymes of
Biological Membranes, 2nd ed.; Martonosi, A. N., Ed.; Plenum: New York,
1985; Vol.4, Chapter 48.
Woodruff, W . H.; Dallinger, R. F.; Antal is, T. M.; Palmer, G.
Biochemistry 1981, 20, 1332-1338.
Woon, T. C.; Shirazi, A.; Bruice, T. C. Inorg. Chem. 1986, 25,
3845-3846.
Wuenschell, G. E. Ph.D. Thesis, University of Southern Californ
November 1987.
Young, R.; Chang, C. K. J. Am . Chem. Soc. 1985, 107, 898-909.
Zimmerman, B. H.; Nitsche, C. I . ; Fee, J. A.; Rusnak, F.;
Munck, E. Proc. Natl. Acad. Sci. 1988,

Linked assets

University of Southern California Dissertations and Theses

Conceptually similar

PDF

A synthetic model approach to H-bonded oxyhemoglobin

PDF

Crystallographic stydies on Zn(2), Mn(2) and Pt(2) complexes of phosphonates

PDF

Crystallographic studies of metal hydrides and other transition metal complexes

PDF

A.The anions of C(60) and its pyrrolidine derivatives B.The search for hydridocobaloximes

PDF

A study of the reactivity between tetraphosphorus trisulfide, P₄S₃, and iridium and other transition-metal complexes

PDF

5-aza-2-deoxycytidine resistance and gene structure in mouse cells stripped of DNA methylation

PDF

Crystallographic studies on new Pt(IV) anti-cancer agents and their reaction products

$Absolute configuration determination of diasteriomeric iron complexes by X-ray diffraction$

PDF

Absolute configuration determination of diasteriomeric iron complexes by X-ray diffraction

PDF

Crystallographic studies on the interaction of nucleosides and nucleotides with transition metals / by

PDF

A comparative study of the chemistry and biology of Heparin

PDF

Characterization of glycoproteins synthesized by human breast epithelial cells

PDF

Carbon-carbon bond activation in platinum (II) complexes

PDF

Absolute configuration studies of molecules bearing chiral methylene groups

PDF

Crystal structures of transition metal carbonyls and hydrides

PDF

A new approach to the problem of measuring the properties of micelles

PDF

Biochemical and molecular analysis of two glucose-regulated proteins (GRPs)

PDF

Chemistry of highly reactive manganese and iron complexes.

PDF

Computer modeling and free energy calculatons of biological processes

PDF

Analysis of the cell cycle regulatory element of a hamster histone H3.2 promoter and its interaction with nuclear factors

PDF

Characterization of H3abp and its binding site: A complex that specifically binds a cell cycle regulatory element of the hamster histone H3.2 promoter

Asset Metadata

Creator Koch, Carol Ann (author)

Core Title Binuclear porphyrin and imidazolate bridged complexes as models for cytochrome c oxidase.

Degree Doctor of Philosophy

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag chemistry, biochemistry,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Advisor Reed, Christopher (committee chair), [illegible] (committee member), Bau, Robert (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c17-651451

Unique identifier UC11342722

Identifier DP21972.pdf (filename),usctheses-c17-651451 (legacy record id)

Legacy Identifier DP21972.pdf

Dmrecord 651451

Document Type Dissertation

Rights Koch, Carol Ann

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA